From what I understand, most of the patronage to Casino comes from the local population, Genting Malaysia, is a good example, where a good portion of the gamblers are local. As for tourist dollars, just imagine, if they were to come from Europe, there is casino over there, from Australia, there is casino over there too, same goes for China, there is always Macao, from US, there is always Vegas. Why would anyone comes all the way from their country to visit Singapore, to gamble away, when they could do it in their own backyard.
I believe, the S$100 levy will be abolished, just a matter of time. As some gambler might say, even before I enter the Casino, I have already loss S$100, levy or not, that's not a good sign or beginning to start with.