Or you could go with the theory, like the old 240z's, are appreciating again. It takes time, but if someone's into owning a car, any car for a long period of time, then it pays to look after it. Also even if for a shorter period, one that's tidy and clean will always sell more easily than a rough one.
But I know what you mean. Really quite annoying is you've spent many hours detailing, only for wet weather on the way to a meet.