We all have different financial means. If you have the resources to do a full restoration, then it should be considered. I would get the car to both the businesses referenced above for their evaluations and quotes. I also agree that it would be very difficult to sell that restored car (right away, or a few years later) and recover the cost of purchase + restoration. Also, would you drive that restored car and risk lowering its value through wear and tear, or worse an accident?
If the rust is severe and is a structural safety issue (unibody construction, remember!) then address it. It may lead to a full restoration, maybe not. Or, you just might sell it to someone with deeper pockets to restore. But, you don't want to drive an unsafe car.
If the rust is cosmetic, drive the car 1,000 miles or more this summer and see if you fall in love with it. Then decide what to do.