I've bought a couple different items with donuts. All said I've probably put $40 into the game. That's sounds incredibly dirty when I say it out loud, but honestly I don't regret a single cent. I don't care if the servers eventually die either... by then I won't give two shits about the game.
I've bought...
Springfield Sign
Hank Scorpio's Volcano Lair + Hank Scorpio
Duff Brewery + Duffman
Otto's Bus + Otto
Hans Moleman
Squeaky Voiced Teen
Plus some odds and ends that I don't remember. I still have 160+ donuts left too.
GR has TONS and TONS of cheats pages (and FAQ pages) for both console and mobile games. Obviously a lot of those pages are written by us, but we don't exactly put them in the content stream. They pull down a lot of readers, but I hope the regulars get some use out of them as well.