I would believe that engineers meet "line" promotion boards along with the pilots. That being said, statistically pilots have a higher promotion rate than any of their other counterparts.
What exactly do you mean aerospace engineering regarding the AF? NORAD, NASA? Or do you believe that you will help design the next generation of jets?
The one thing to understand about being a pilot, is that every airframe has specific bases. Cross over is not common unless the jet is being boneyarded or you took a bad juju assignment and it is payback.
For example:
Fly the Strike and you will spend your life floating between Mt Home, SJAFB and Lakenheath. If you are the top of the game and go WIC, you could sprinkle in an assignment to Eglin or Nellis, but that is not the norm. The norm is rotating among the bases that jet is at. Bullet went SJAFB, Elmendorf, SJAFB, Leavenworth, Pentagon (desk assignment) and back to SJAFB.
When he was with 111 it was Mt Home, UK, Cannon, UK for the majority of people.
Do not enter in as a pilot believing you will be able to x-train and fly different jets as you would buying a new car every few yrs. You are not likely to have the career progression of flying a 16 for 4 yrs, get into a 22 for the next 6 yrs and spend the final yrs in the 35. It is possible to x-train once, but the majority of people start their career in one plane and finish it in that plane.