What can I do if I want to publish my PhD thesis work as is, but my advisor wants months of additional work?
As usual, the first piece of advice I can offer is to talk to your graduate advisor to get his take. That said, it sounds like you're getting advice which will increase your chances of getting a paper accepted from people who have experience in the field.

Your theory that they're asking you to do work related to a "hidden agenda" seems a little far-fetched... when considering the extra analysis, writing it up, and publishing, you're looking probably 18 months into the future. Your committee is well aware of this. The likelihood of all that happening in any timeframe that would be beneficial to them is pretty darn small. Even more so, they have their own students who can work on their stuff. They wouldn't hang their hat on the chances that a graduate student who has already moved on will do some research that may or may not result in a publication. Long story short, I wouldn't worry too much about ulterior motives.