Been a long time watching this question hang there, and I'm not sure why it hasn't gotten more action, except that most of us aren't that experienced in Gretsch. My current kit is my only one ever.
I suspect the best bet is to look at Gretsch history, to find out who was making them. Around 1970 Gretsch sold out to Baldwin (pianos), and according to the Gretschophiles that was a watershed. Round badge (RB) Gretsch's were made until that year, and are all considered great, whether they deserve it or not, and the prices reflect it, particularly bop kits in original condition which can fetch up to 10 grand. Some time in the late 1980s Gretsch (the family) bought the company back, and that has made all the difference, again according to the cognoscenti, but early RB remain the most collectable.
The company history is probably fairly interesting. This link below is a bit of self-promo for Gretsch, and some of what went on is indicated. I don't know what's going on in those factory vids, whether the drums are out of round or the machinery runs out of true -or both- but I sure wouldn't let anyone see that. On the other hand, maybe the secret of Gretsch's success is wobbly everything.
There are also different shells, made by Gretsch and by Jasper (Jaspar?) (a furniture company); but you'll have to investigate the gossip on all that:
http://www.youtube.com/watch?v=qkGWv2rz ... r_embedded