I'm not sure where you get that idea. There isn't plenty of undeveloped land unless you're talking about jurong or punggol, and it doesn't help if those places take 2 or so hours to commute to downtown from on the MRT. If you're talking about the small patches of parks and the historic heritage sites, I think they have their reasons for keeping those.
It doesn't? It's 53 min from Tuas Link at the extreme western tip of Singapore to Raffles Place by MRT, and you'd be hard pressed to find a place in Singapore where even a connecting bus would add more than 30 min to that.
Either way, I'd argue that you need some parks and forests, or your populace will go insane. 20 or so golf courses in such a small and dense island are ridiculous, though.
