Are the old school steel body cars out dated compared to the new fiberglass cars?

It will seem that way because most of the top teams will switch to the new bodies.

Cool factor alone makes them good. If I'm not mistaken, the replacement panels (god forbid you need em) are reasonable too.. and easily found. Not like waiting for Cross Canada's nearly a week long run for one fender.

I don't know much about the tech end of this stuff, but if there are cars that will be obsolete, I don't think its because of the body style. You can keep that even just with weight.

You're right Shadowracer, you don't know much about the tech end of this.  :DThink of this as a parallel to what happened to the Cascar based cars that ended up as the current late model.
It's the same thing that has happened at every race track in North America.  Class requirements change,  rules are adjusted, cars evolve.    The details might be different from class to class and track to track but the process is very similar  and the end result usually is the same.  Most of the cars will be obsolete if they don't change.

With the Delaware Super Stocks it's not just the body but the whole package that makes the difference.  I don't think these are done evolving either.