I don't know your Espire, so can't give you any input.
The 6600 and 7700 are very similar ... 7700 has the bigger throat space and a couple more bells and whistles. However, there are a couple on the 6600 that are not ont he 7700.
I bought the 6600 a little over a year ago and while the throat space seemed huge to what I'd had, I am already thinking I want something with more space. I've been considering the 7700, though do not see it as much of a jump to what I have, so have been holding off for now. Need more time to do the education part for an informed decision if and when.
The comment you made about your dealer would concern me more than about the machine switch. That being said, I have no idea how the Babylocks and Janomes compare in general.
If you have not been pleased with the service for your Babylock ... would you really think it would be any better on the Janome, when you are dealing with the same people?
I understand your problem though ... local dealer is very important to me too ... though quality of service is more important! JIMHO