To be honest, there are some cases I have not expected to get answers. Non-homind fossil sites have been one of them. I think a) you have to be a good expert in this field to answer the raised questions and b) although the community accepts their importance, these sites are boring for most of us so that people are not interested in discussing them. But I wanted to make a try. Thanks.
Am perfectly prepared to discuss. I am not sure whether I am in sympathy with the objective but, herewith, a few thoughts for you to accept or reject as you wish! In any case some extra "knowledge", understanding or insight might emerge!
IMO, Palaeontological sites (PS) are not so much "boring" as not being really suitable for WHS inscription. They must be the only WHS where all the known heritage objects have been dug up and taken away!! Does one visit them to see where the objects were removed from - which doesn't seem very productive - or to see somewhere where there may (or may not) yet be more similar (or even as yet unknown) finds - which also seems a bit "mystical"? I know that "World Heritage" isn't (or isn't supposed to be) about people "visiting" the sites - it is (or should be) primarily about preservation. Clearly any area of fossil bearing strata which records an aspect of the World's geological/natural development, and may yet yield more, is worth preserving but, for better or worse, the visibility of an inscribed WHS IS important and Fossil sites don't really provide that possibility. Other schemes such as Geoparks could adequately carry out the preservation and educative/interpretive functions.
Many existing PS are really only worth visiting for the nearby museums. I think of Monte San Giorgio - the museum in Meride is very fine, both for its contents and as an example of the work of Mario Botta - but its location "on site" isn't really essential and can be seen primarily as a "tourism attraction" feature. And Italy's "extension" for that site is undoubtedly driven by its race to try keeping up with China's WHS count!
We have visited a fair number of PS (both hominid and non-hominid) and I can't say that, beyond the museum, they have proven memorable or even worth while. Even Olduvai didn't really add much, other than a wonder that they were able to find anything there!! One minor exception was at Messel Pit where, although it wasn't a part of the normal tour, our guide kindly took us further into the pit to see examples of the strata being split and examined by a research team. Another was a Dinosaur Footprint site in Korea where there was at least something to see still in situ - and a nice (albeit "general") fossil museum. The reality was however that it was run as a theme park on Dinosaurs for kids – and IUCN has already told Korea that it doesn't think much of Footprint sites!
So, if one isn't drawing up a "dream list" of sites to "see/visit", what about a list of "dream sites" to be preserved (whether as WHS or under some other protective scheme) - what criteria should be taken into account? You suggest "Achieving an overview of the development of the World's animal and plant life
". There are "overviews" .... and "overviews". Just (partially) covering the current range of nature on Earth has already taken around 250 WHS. And to try to cover its development since pre-Cambrian times across the range of ecosystems and types of life forms across the continents then existing adds another major dimension.
As an example of the problem of choosing. You debate the potential representative site(s) for the Cretaceous. This period is of course "famous" as the era of the Dinosaurs. The obvious choice would be to go for somewhere where good examples of the iconic dinosaur megafauna of the Late Cretaceous had been found. You suggest a choice between Canada's Dinosaur Provincial Park and a selection of Dinosaur sites from Nequen in Argentina (Though Mongolia might have something to say about that!). But isn't that a bit like representing the entire Holocene by a selecting a park containing the "Big 5"? We really need to cover, inter alia, birds, plants, mammals, fish, reptiles etc etc etc all of which underwent significant development across the period even if they are not as "exciting" as Dinosaurs!.
What other aspects of the Cretaceous period could be considered? One significant geological aspect was the relatively small area of land and the existence of many shallow marine areas. So why not consider sites in Colombia which has some fine fossil areas which cover the Cretaceous fauna of the proto-Caribbean? If you are into early Crocodiles and Turtles then this is the place for you!! If it is "BIG" that you want then you can visit the Museum at El Fosil which consists of a single example of a large, albeit baby (!!), Kronosaurus. The area around Villa de Leyva is excellent for marine fossils from the Cretaceous and they are nicely shown at the Palaeontological Research Centre. Are sites which yielded fossils of Dinosaurs more "dream" in your opinion than those which yielded Crocodiles/Turtles etc?
It could also be said that almost the most important evolutionary development of the Cretaceous was the emergence of small mammals which could develop post KT. Shouldn't a Cretacious fossil site have such examples? Perhaps, the best choice of site to "represent" the Cretacious should be one with a mix of faunal types from the period rather than just Dinosaurs? I understand that the Hell Creek area of Montana yields such a range of fossils.
This forum is about WHS so it would seem best at least to look at the current T Lists before bringing in other sites! I have had a quick look through the current T Lists for their hominid PS (I may have missed some as the titles are not always explanatory and I didn't check every T List site unknown to me). I found 17 or approx 1% of the total T List. The Cretaceous in general and "Dinosaurs" in particular figure frequently and "footprints" are popular! What do you think about them? Are there any gems awaiting nomination – or yet more dross? I have indicated the period from which the fossil OUV is being claimed.
Pehuén co - Monte Hermoso (Arg) - Cenozoichttps://www.worldheritagesite.org/tentative/id/5851
Flinders Ranges (Oz) - Cambrianhttps://www.worldheritagesite.org/tentative/id/6524
Cal Orck'o: Footprints of time (Bol) - Upper Crethttps://www.worldheritagesite.org/tentative/id/1816
Guizhou Triassic Fossil Sites (Chi) - Triassichttps://www.worldheritagesite.org/tentative/id/6381
South of Ricaurte Province (Col) - Cretacioushttps://www.worldheritagesite.org/tentative/id/5771
Tatacoa Desert (Col) - Cenozoic (Miocene & Pleistocene)https://www.worldheritagesite.org/tentative/id/5766
Moler landscapes of the Liim Fiord (Den) - Lower Eocene/Paleocenehttps://www.worldheritagesite.org/tentative/id/5474
Bosque petrificado de Puyango (Ecu) - Mesozoichttps://www.worldheritagesite.org/tentative/id/1081
The Ipolytartnóc Fossils (Hun) - Neogenehttps://www.worldheritagesite.org/tentative/id/1502
Eocene Marine Biodiversity of the Alpone Valley (It) - Eocenehttp://whc.unesco.org/en/tentativelists/6539
Cretaceous Dinosaur Fossil Sites in the Mongolian Gobi (Mon) - Cretaceoushttps://www.worldheritagesite.org/tentative/id/5944
Paleontological Sites of Pisco and Camana Basins (Per) – Neogene/Paleogenehttps://www.worldheritagesite.org/tentative/id/6418
Sites of fossilized dinosaurs throughout the Southern seacoast (Kor) - Cretaceoushttps://www.worldheritagesite.org/tentative/id/1640
Sinpetru (Rom) – Late Cretaceoushttps://www.worldheritagesite.org/tentative/id/559
Le Permien marin de Jebel Tebaga (Tun) - Permianhttps://www.worldheritagesite.org/tentative/id/6087
Dinosaurs and Caves of Koytendag (Tkm) - Cretaceoushttps://www.worldheritagesite.org/tentative/id/5434
Petrified Forest National Park (USA) – Late Triassichttps://www.worldheritagesite.org/tentative/id/5253
I have not included a T List site from Tunisia titled "Le Stratotype de la limite Crétacé-Tertiaire (limite K-T) " because, unlike the Stevns Klint inscribed site, the T list description makes no mention of fossils but concentrates on the mineral remains containing meteorite elements. Though it is not clear why there should be a difference See - https://www.worldheritagesite.org/tentative/id/6088
. Could it be worthwhile having an exercise to assign a "Category" to each Tentative site. This would enable the 1725 to be examined more easily by type and could throw up some interesting data on the number of "me too" sites of each type and the presence of genuine value and novelty. We could start by using the same Category list as for inscribed sites?)