Project Boat vs Bare Hull
A couple of things to add.
First a lot depends on what you can get the 15 - 20 (or older) boat for. If you pay too much and put a lot into it you will never recoop your investment.
But then again boats are hardly good investments. I bought mine as a vehicle to an enjoyable lifestyle. I am sure thre are those who actually ''make money'' fixing up old boats - of course not sure what they end up making an hour and there are probably fewer of them then those wishing to make money in resale.
For me it was a matter of a limited budget - buying an old boat that can go sailing now but needs this and that. which I will do as we go along. In the end it will cost less than had I bought a newer boat and had the resale price drop as I used it. I may spend more time fixing though - at least in the beginning.
Also rember that one man''s project is anothers routine maintenance.