My kids do the same. They get a set, build it, play with it for a while, and then it gets deconstructed and mixed in with the Big Bin O' Lego. Oddball pieces become wings, or arms, or showerheads, or whatever their imagination sees.

To me, that's the spirit of Lego. Even as a kid, I had friends who had, e.g., the Space Shuttle set, and once that shuttle got built, it was sacrosanct. If I tried to pilfer something from it, a blood feud would ensue.