hifi as investment?

Well sort of. I am just starting out in this hobby and having already exchanged a few used components I bought here and later sold- sometimes for the same amount I paid- sometimes for more-

Seeing this has made me consider the idea that one could approach this hobby's acquisitions as a sort of currency. Considering the ease with which many popular components are sold- SCD-1, De Capos, etc. I have begun to realize that it is possible to approach an expensive system with the rational (if art is not enough) that ridiculously expensive components are just another form of money- a temporary resting place for your reserves (of course this considers purchasing used and at a fair price).

I'm looking for nominations. What components are most depreciation proof once they have taken the hit of being used? I want to rationize an absurd purchase and enjoy my monetary reserves while retaining my safety net.

Does anyone else approach it like this? Used Elrods? Don't get me wrong, I'm doing it for the love of music, but a $15000 system requires some consideration of financial prudence right?