I would re-evaluate every three years. Twice, I seriously considered leaving and had interesting offers. The problem was the company I worked for was the industry leader, and even though I was a consultant, I really had nothing to compare this job with. I was kind of like you in that I had no feeling one way or the other whether I should stay or move on.

I finally left after 12 years to raise my kids in a better environment. I realized later I had been hard core burned out for at least three years. For me, more change is better.