I agree with your first point. TJ hard tops generally go for $300 to $400 around here. I've seen LJ tops go for the same but that's rare. Double the above is probably more realistic.
Regarding your second point, there are plenty of rust free cars up here. It really depends on how they were driven and taken care of. Most cars are driven with no long term plan of keeping them (not surprising) but a lot of them are babied from new. My XJ & MJ are good examples of that. They were never the previous owners' only vehicle and they survived nicely.