We have made a few connections through CLT (not to MBJ) and never had a problem. It's actually a nice airport and a manageable size if you have to run from one terminal to another.
Like Philly, CLT is a former US Airways hub so you are now stuck with AA for most of the flights. I have been watching the airfares as well, and have noticed they seem to be increasing. What's interesting, however, is direct flights from PHL to Cancun are now very cheap (in the low $300's, which is competitive with the low-cost airlines). Wonder why these flights are roughly half the price of MBJ flights for a trip that is a similar travel distance. Is the demand that low?