Thanks a lot, Bobby! Unfortunately I can't play an instrument. Wish I could, because I always get goosebumps, when I hear the slighly overdriven Hammond/Leslie Combination. I'd love to play such a monster. Well, that's why I used to "sing" in a band, when I was young.
Cup rings and cigarette burns would indeed have been a nice addition. I already tried to make it look used and a bit worn:
Additional to a scratches-texture map the organ has a dust layer on top of the other surface layers. That's a cool thing to do, because you don't need to care about textures. I just added a surface layer after the parts shader with a slope constraint (Final normal, Use "Y"). It can be constrained by height as well, and I didn't test intersect underlying, but this could be interesting too.
As a nice side effect the dust looks like the coating is a bit chipped off at some places like the board where the pedal is.