I was always under the impression that once Acceleration hit the stores that tweaking FSX was no longer an option as most if not all of the tweaks we used for the base FSX had been incorporated into Accel.
Also, after running FSX/Accel for a year now with no real problems except maybe being unhappy with the FPS I get (and that speaks more to my system than anything within FSX), there's no way I'd start over again from scratch on the off chance that I might see a few FPS more. I guess that's what it becomes though with every system different from every other system. . .the pursuit of the "Almighty FPS", lol.
If, on the other hand, there are tweaks that I can try without wiping FSX clean and starting over. . .I might give those a try. . .I just assumed that once I had FSX/Accel/SP2 installed. . .I was pretty much "There".