I love reading John Rosemond, my favorite parenting author. He has said that kids should have very few toys, and the toys they have should be very plain and simple, such as blocks, legos, tinker toys, bike, ball, etc. Otherwise, instead of using their imaginations (the block can be an airplane, a monster, a ship, etc) they play with toys as they are for a few minutes, and then are done. Check him out at www.rosemond.com. I get his books cheap on amazon, or check the library.
He gave an example in one book of some parents who walked in on their kid in his room while he was lavishly pretending that some item in his room was a rocket, and he was having a ball. So they went out and bought him a rocket to play with. He was bored with it in five minutes. Same at Christmas time, all these very specific toys that do one thing become boring fast, and the day after Christmas the kids are moping around with nothing to do. And, the gift givers (namely Mom and Dad) are frustrated at all the money they spent, and the mess to clean up, and the expensive toys that break and aren't cared for.
My six year old has spent hundreds of hours playing with his blocks, cars, dinosaurs and legos. And he and the three-year-old spend hours outside playing in the $6 pool we got at the end of the season, or on their bikes/trikes.
If your son doesn't care enough about them to take care of them, get rid of all the broken ones (I know it's hard!) and take away whatever else he won't keep cleaned up. Give it to charity, or let him earn them back one at a time. If grandparents and such ask what to give for Christmas, zoo memberships and such are wonderful, or else toys that truly have a lot of play value.