I have a 2002 Calfee carbon fiber frame, with aobut 45,000 miles. If I replace it with a new one, what improvements can I expect? I have no complaints about the frame, other than a poor paint job.
Highly dependent on the manufacturing process, of which there are a handful of categories and endless variations. Most carbon frames these days are some variation of the monocoque process, and if I were to venture to guess I would say your 02 Calfee is carbon lugged carbon tubes- so there's one difference. Given the brand that you currently own I assume you'll be looking for a high end replacement for it. You're almost certainly going to find yourself looking at lighter frames, but over the last few years many manufacturers have started focusing on improving ride quality over weight savings of their top of the line frames. You'll hear the terms "lateral stiffness" and "vertical compliance" a lot, as those are 2 of the primary qualities (but not the only qualities) that make for a good riding, good handling bike. These are the areas where you should see the most improvement over your current frame. On the other hand, if you're happy with your current frame beyond the paint, maybe you should consider getting it repainted which Calfee themselves would help you out with, or at least get you pointed in the right direction.
if you'd like a more in depth description of lateral, vertical, and torsional stiffness and compliance, and how bike manufacturers try to balance them all out read this article.