My parents saved things that they knew would last almost forever like our Fisher Price Little People. The Little People are different now, but still built to last. For our kids, we've saved the Weebles, Little People, and wooden trains, and a few other very young baby toys. The Barbies are kind of messy; I don't plan to save them except for ones she wants to keep herself (my daughter is 8 so we haven't gotten rid of a lot of stuff yet), but there are other toys from that age range that have more staying power. Nothing with batteries. Although a Wii is nice for friends visiting with teens, if its not used often, I wouldn't be confident about it working when I pulled it out, so I definitely support your decision to sell it, unless you yourself like to play with it, or one of your kids wants to move out with it.
Someone else mentioned a pack n play. We do keep one in our attic for houseguests with babies, and we've kept a portable feeding seat too. It's come in quite handy for friends visiting, but I'd only recommend if you have good attic or basement space.