Our kids are big Lego and block builders. For the past 6 months it has been their #1 choice for play. But the unfortunate part is that they want to save the creations, then slowly "lego erosion" takes place, and the little pieces wind up all over the floor and the masterpiece is broken. Or we end up with a tower of blocks in the living room which I inevitably trip over and knock down, ending in a finale of tears (not mine).
To resolve this issue, I've started taking photographs of my boys creations. This way we can document what they've made, and are not upset when it's time to disassemble them. I also think it will be fun for them to look back in a year and see what they made. I think this method can work with artwork, clay, or any other creations. The main point is the process and the fun of it, but a keepsake is also important, and the reality is — we can't keep it all.