I guess I'm labeled "unusual" in this thread, as I actually value throwing stuff away as the build progresses. It's almost like a sense of satisfaction. I only do aircraft kits, so all the box tops get clipped with just the plane picture, and hung on my sons wall. He's got quite a nice little dogfight scene happening in his bedroom. Sometimes I'll have to use the razor knife to trim some of the stuff, but it's a small price to pay, and he and I both have something to look forward to at the end of the build. I build for a guy in Michigan who sends me kits to do commission work for him. A lot of times, he'll stuff a lot of kits in one box, and expect me to sort through it all, but I've learned to deal with it. I have maintained a few extra box bottoms to be able to give some of the loosely placed kits in a home of their ow, but when they're done, I pitch it. Instructions, all spare parts except for weapons, seats, consoles, and pilot figures. The first part of the fun was obtaining the 100 kits that I now have in the stash, and I get equally as much enjoyment now by slowly starting to see some room start to open back up in my closet as I get rid of the old stuff. I have also put the red light on buying anything new for quite some time, as I feel like I have everything I want to build in front of me. The challenge to me now is to completely empty out the closet. In the past 12 months, I've completed 30 models, so it doesn't take long to see progress.
As for the spares and such, do yourself a favor and go to Wal-Mart, and spend ten bucks on two of the plastic containers with lids. I keep all my spares, decals, and other random stuff in these. And every six months I'll go through it and evaluate how important some of the stuff still is. If I don't need it, or haven't remotely come close to using a part that's still being saved, then I pitch it. I prefer organization over collected chaos anyday.