Personally I've had a blast last few nationals I've been to. Even if I don't find anything to spend $ on, its always interesting to see what's out there. 2 years ago in Chicago I spent only $9(on a fleece sweatshirt ) but last year I dropped close to a grand. But I had just as much fun at both. If your into 'large pieces' (16x20, Jerseys)you'll find all sorts of stuff being dumped at below market prices. Some manufacturers that do card signings over the year also get some bigger stuff done and sell it at the national at really good prices. Some of it is plain crap, but some is actually stuff you'd hang up.
if I get over this cold that's had me on the shelf for days, I'll be in Chicago.