I think the set up of the voting may lead to some of those underwhelming sites getting some backing.
Possibly, though it depends on whether they used the checklist to guide their list, or whether they developed a list beforehand. My strategy was the latter, which I approached by evaluating one region at a time (Australia and Pacific; North America and Caribbean; South America; Africa; Middle East; Asia; and lastly, Europe) with nominal caps on sites chosen per region to help narrow down the list. Even with this strategy, I found the categories for the most part were well-represented (save for Rock Art where I chose none of the sites listed in the category, but instead relied on sites I selected from other categories that also have rock art components).
Ultimately, it turns out I selected more natural and mixed World Heritage Sites combined than WHS from Europe, so I was happy with the Top 200 I selected. I'm curious how my Top 200 will evolve as I visit more sites worldwide, though.
Also when it comes to the final count is it worth thinking about combining the votes for Contiguous Sites?
That's a very good point, particularly for those two examples you mention which are each rather ridiculously treated as two separate World Heritage Sites (the French extension to the Route of Santiago de Compostela also comes to mind...). If you combined votes, though, how would you treat the selections from someone who voted for both contiguous sites (i.e. Iguacu National Park and Iguazu National Park)?