... Anyone been able to actually talk to the reps at a show like this and have a conversation? ...
Not many WGH shows in my area, but the two I've been to the reps have been interested in serious exchanges with informed hobbyists on current topics. Their eyes tend to glaze at the "why dontcha make X?" approaches.
I especially recall one such encounter with an Athearn rep at a WGH. At the time I was aware they were about to take over McHenry couplers and he was interested in discussing their plans, which were much more involved than how it actually evolved. I had waited behind a fellow who wanted to chew his hear off to push his need for XYZ (obscure small RR) coaches, why couldn't they do those. The rep was polite, but both he and I rolled our eyes at the out-of-left-field request after the gentleman stepped away.
In so many words, they want to talk to you, and it really helps to be knowledgeable about their products. With Walthers, yes, thank them for adding to their N scale selections and then make your pitch for "...it would be great if you ported your HO [such-and-such] building," etc.
OTOH, the Scale Trains guys run for cover whenever they see me coming, 'cuz they know I'm going to ream 'em out about couplers. Again.