I think many restorations are done to preserve a gun, not for financial motivation. I know that was what prompted my "Clunker Optimus" project some years ago, and has me starting on another similar gun which is literally blown up right now.
http://lefeverforum.informe.com/clunker-optimus-dt514.html I think you'll find the pre-auction comments from my collecting friends amusing, as I did.
I enjoy the process, and limit my rate of expenditure to what my bank balance allows. My "losses" upon sale over the 50+ years I've done this are probably less than on my stock market "investments" gone bad and my new car post purchase depreciation.
I don't think it is reasonable to expect to profit from a hobby!