Yep I've got the Costello and it is to die for!! I've never played a real vintage one though so I can't give you a good direct comparison. And while I found nothing wrong with the standard PUPs I did switch 'em out for the Lollar Jazzmaster PUPs which are just exceptionally great. Novaks are incredible too.
The bridge did give me the typical JM trouble, but basically right as I was getting fed up with it and looking into buzzstops & alternate bridges and such the Mastery Bridge came out and I got one. Its pricey for a bridge but I've never had any kind of issue with buzzyness or anything since I got it set up and intonated properly. Definitely worth it for me, if for no other reason that it put my mind at ease about all the typical JM bridge complaints (and the complaints about buzzstops "dulling" the tone, and mustang bridges being a step up but not a 100% fix).
Check out
http://www.masterybridge.com/home.html, those testimonials certainly sold me, seeing as how those guys are all huge influences on me and big parts of why I even wanted a JM in the first place... so if its good enough for them...
Most people hate the cosmetic changes I did to mine but I freaking love it, very unique and plays/sounds like an absolute dream. If you can swing the Costello I'd definitely do it--Elvis' specially designed trem is amazing. It doesn't swing freely and still hold in place though--something to keep in mind. I've gotten very used to playing with the trem in my hand about 80% of the time and very quickly knocking it out of the way when I'm not using it but I know a lot of people really need it to just fall freely out of their hands.
ahh... happiness-
My BJFE- Some special ones. Some standard ones. I love them all just the same.