We don't have this same problem with legos, but my daughter seems to have some SERIOUS hoarding tendencies. We have to implement limits. Her personal favorite is keeping paper! Doesn't matter what it is, she wants to KEEP IT ALL. So, when a big stack of stuff comes home from school, I tell her she can select FOUR items to keep in the drawer in her room - the rest go into the recycling. She's gotten a bit better, thank god.

~amy