I have one random lego knock off item on my shelf, it's a monkey. I don't particularly like legos, or monkeys for that matter, but I keep it because it was pretty fun to build it and it reminds me of that.

Seems like you could amplify this by about a million with a set that is both intricate and of a subject you are really into.

Or disassemble it and make new stuff. As a kid we never had sets, it was all in a big pile.