I collect strange plants (mainly epiphytes, but I'm branching out a bit). I also collect original paintings I find at thrift stores, regardless of how much some of them suck.
It would seem that I collect empty tin cans (steel cans, technically). Coffee cans, tobacco cans, holiday popcorn/cookie tins, etc... I only just noticed this, looking around my room. I have stacks of the things and I'm not sure why.
I collect musical instruments, though not as extensively as my tin can collecting.
In terms of the plants, it's purely intellectual with a smidgeon of the aesthetic - as a result, but not as a motive for the collecting itself.
For the tin cans.... I have no clue.
For the paintings: some of them are actually rather good.