You should get some diffusion of the higher frequencies with a pop corn ceiling but unless you have really high res stuff, an optimized listening room, really well developed listening skills, and are a bit on the anal side of neutral, you would probably hear no difference. :-)
Popcorn Ceiling vs Smooth
I am in the process of remodeling/updating a home we just bought. My wife is having the popcorn ceiling removed in the whole house. In, what is to be my dedicated 2 channel listening room, I have the option to leave the popcorn ceiling or have it smoothed out. The room is 14x17 with 8.5 ft foot ceiling. Does anyone have experience or recommendations on which way to go? I have done a search and cannot find much on this topic. Thanks