I do a first level filter when it comes home (is it really that good/cute/etc.) My kids are younger so that is easier to do b/c some of it is just scribbles. We also live away from grandparents so I mail a lot of these 'gems' to grammy and grandpa!
I also read once that a good way (and I will be doing this when they get older) is to save what you want throughout the year in a bin and then at the end of the school year you pick a number (3, 5, 10, etc.) that you EACH get to 'pick' to save for their forever box.
I love this b/c it serves two purposes, it keeps the clutter down and more importantly it helps teach the child about organization, learning to edit, gain an understanding that 100% of everything really isn't 'important'. It sets boundaries, and helps build an understanding w/in the family that there are choices to make and that some of them will be harder than others. All of which will come in handy when the choices/ decisions are of greater consequences when they are older. Think of it as a skill building exercise!!