Clean Paint applied by a professional body shop is always a good idea, In my book. As far as increasing the value of a vehicle for sale you wont see the ROI. If hes family and he is going to do a nice job for cheap then I say let him do it but dont go choosing a NON-Subaru color. That will put you into a very niche market when you try to sell it. Clean Paint and a clean interior usually adds about $500 to the perceived value of a car.
Not worth it if your selling it but worth it to feel good rolling around in a freshly painted ride : )
13 WRX Hatch - Cobb OTS Stage 1