I usually just think about the game i want to replay and if i can't replay the story clearly in my head i'll say it's worth doing. I have no idea how someone can play through a game two or three times in a row. I would get so bored.
If you asked me how many times I've replayed Zelda: Majora's Mask, I'd start laughing my head off. No, not because I'm crazy, but because I lost count after 7. I've replayed Rune Factory 3 about 4 times now, and I'm on my 6th playthrough of Zelda: OoT. And that's my answer. ._.