the San Antonio Missions expect a moderate economic benefit to the park
Actually I thought that argument was the weakest part of the piece - "One study suggests that merely adding the San Antonio missions as a site would generate well over one year's annual US Unesco dues – more than $100m in economic development."
It doesn't state over what period this $100 million in economic development would accrue. The implication is that it would occur each and every year so as to match the annula UNESCO amount. If this is so then presumably they assess the number of extra people who would visit the San Antonio area because of the inscription and multiply this by the amount they would spend on average . So - 500 extra people per day is 182500 "people days". If each spends $400 per day on hotels, meals, entrances etc this is approaching $80 million. But that would not be a net gain for the whole of the US since many of those people would presumably have spent their money somewhere else - apart from all those who were going somewhere other than the US for their vacation and only came at all because of the inscription (in which case of course their entire net spend across the US could be counted) but there would not be many of those I would have thought.
If it is a "one off" from extra investment in hotel rooms/restaurants etc to cope with the increased numbers then it is really irrelevant to the annual UNESCO figure.
In any case the issue isn't about money of course - which is why I find such simplistic comments, which at face value seem unarguably to clinch the issue, actually weaken the case being made!
Regarding the "economic benefits" of inscription - I have never yet seen a convincing case made from a "Western country" with an existing well developed existing tourism industry. UK did a reasonably thorough consultancy study and failed to find anything significant. There may be a "substitution effect" versus other destinations in the country but that is still largely a zero sum game.