I'll give your questions a shot. I can't answer #1 about changing the flapper, but from what I've read about the Toto Eco models, you won't need to. #2, Sanigloss is probably a nice feature, but I have no personal experience with it. My Toto Dartmouth did not have it as an option, but I have had not problems keeping it clean. #3. I have the softclose seat and have no problems with it. This may be a personal opinion matter. Seats are standard, so you can get what you like. #4, Toto's are not a bargain basement product. You will pay more for a toilet that does not clog and is easy and inexpensive to maintain. My best advice is to check Terry's Report on Low Flow Toilets and see what he is selling them for and use that as a guide. I wouldn't expect to find prices much, if any, lower. I suspect Toto dealers would all price their toilets in the same ballpark. One thing is for sure, you will save on the cost of a plunger!