4000 grit Abralon is not polished, though it's fine enough to look it. Even 1500-2000 grit has a lightly polished look to it.
As for the SG, use it like any other cleaner. Spray it on a rag and wipe.
Your coach is telling you to use an illegal cleaner. Acetone should not be used on a ball you use in sanctioned competition, and it's been illegal for some time. I'm sure your coach is aware of that and just doesn't care, and there's probably little you can do to stop him, but you are breaking the rules using acetone.
Standard acetone disclaimer: We get this every other month. It's illegal. It's a very strong cleaner and does a very good job (so I've heard). Every shop keeps some in the back for getting belt marks and glue off a ball. Doesn't make it right. It's illegal and that's the end of it. Doesn't matter if the rule is outdated, if it really doesn't have an effect on the surface or integrity of the ball. It's illegal, period. You don't like the rule, get it changed. Or be a dirty, filthy, stinking cheater.
Alcohol or an SG mix after each set is a good idea, with a monthly or bi-monthly cleaning with a real strong cleaner is an excellent maintenance regime.
SH