I would not use solvent. It would be hard to get a uniform result using solvent in my opinion. Also, solvents will melt away sanded/molded sandpaper like surface and make it shiny at best.
I would think sanding is better choice, but it also has problems. I heard some stories about using sandpaper, and most of them were complaints(results not uniform, too tired to sand them, and etc) You would probably get better results using sand blaster, but that is a lot of investment for the purpose.
I would personally recommend getting a set of blank caps. PBT will be better than ABS.
