I think things are fine the way they are.

The downsides are that places that are frequent destinations (like Vegas or Orlando) will make up the bulk of the posts in a forum and will drown out discussion on other locations.

I'd support the idea of adding some non-US city forums, if there was any city that really had significant traffic in any existing forum. London is probably a good example, with a lot of posts in the UK & BA forums (though much of the content ends up being irrelevant chat that belongs elsewhere).