I had my Al frame sandblasted and then powdercoated, both "not recommended" for aluminium. Sandblasting, if not done carefully enough, can remove a bit too much of the material, as Al is far softer than steel, and some say that the heat treatment of powdercoating can weaken the welds by cancelling out the factory post-weld heat tretment... Anyone has reliable info on this?

The frame is now fine, I will report back in two years...

Of course, if you want liquid paint on it, and dont mind ~100 grams of extra weight, you can leave the original paint on as a primer.