To be honest I don't remember getting 100% in any RPG. I've been playing since I started Phantasy Star II in 92, but even when I fall in love with a game I'm more likely to replay it after a year or two than go for 100%. Maybe it's because the games I really started with didn't have 100%. Did I miss a chest in PSII? Likely. But there wasn't a menu screen showing percentages to make me go nuts over it. I think it was the 3rd or 4th time I played Shining Force that I realized you can get Arthur to join.
I love the Disgaea series... but even there I never got everything. Got all the maps, ground thousands of levels and reincarnations.... got bored with it before UB4. Depending on the game the best part of most RPGs for me is either the story/characters (Lunar, Grandia, DQ, FF) or getting my arse handed to me by someone and coming back afew levels later and triumphantly passing out stab wounds (Disgaea, Gothic, Risen). Being able to explore and find hidden places and new weapons is always a big plus, but I've never seen any reason to insist on finding *all* the items, or having one of everything in inventory.
I'm old now, and married as of last April. Between work and a wife I'm grateful to get to finish a game every now and then.