I disagree - the dual pricing for foreigners hardly makes a difference. Also, with a Thai DL and/or WP most private companies will give you the local price. Interestingly though, I once visited Bang Pa-In palace (operated by the BRH) and they wouldn't give me the local price (go figure). However, they did publish their income lat the entrance which I appreciated - on the day that I visited the figures for Thais to date was 30 million and foreigners 900 thousand - had the foreigners been charged the local price, it would have been 300 thousand (hardly a big dent in the overall scheme of things). I would assume that similar trends would be noticed at national parks if they published the figures i.e. most income is feom Thais.