I don't have any direct experience with the Mx docs, but I'm sure others will chime in with their experiences; the only one that comes to mind who has a good following is Dr. Sauceda.
My perspective on this is that with plastics it is preferable to keep it local if at all possible. This is not a MX vs. US thing, but rather a travel vs. local thing. Plastics, particularly getting into body lifts and the like, have a much higher chance of minor to moderate complications than your original WLS. Things like incisions that don't heal promptly or open up again, lingering drainage issues, seromas forming, etc. Much of this can be handled via pictures and email but other things are better handled with an office visit. It's usually much better to have the original doc handle these things than trying to find a local third party to do the pickup for him. It's one of the things to consider when weighing the costs of travelling vs. local care.