Well ok, that's not strictly true as I've bought a slew of new parts yet to be installed on my car since the restoration has not yet begun, but they are things like brake lines, shoes and calipers, shocks etc. Things that need to be replaced or upgraded like adding AC. But for durable parts like valve covers or steering wheels, I have only the one.
Years ago I was heavily into air cooled VWs and I had a lot of everything. I built a couple from parts. There is a significant cost to storing parts from a number of cars and I'm not wanting to tread the same path with the E9. My wife is very accommodating and supportive but our house is small and car parts are forbidden in the kitchen. So I'm trying to get only what I need and no more. A fine line.