I did see a video on a guy using the acetone method on PLA; although this is most commonly used on ABS and most people say it won't work on PLA, it looks like it worked to a certain extent...he printed in black PLA and when the acetone dried it turned some of the pla a whitish color... so if you're worried about the pla changing colors this wouldn't work....he also didn't vaporize the acetone, he just STRAIGHT dunked it in...I'm not sure if I would go that route but...
Anyway you can find the vid on youtube, probably type in trex pla acetone or skull pla acetone.
I haven't done much research on finishing pla yet, but I know the bondo/sanding/wet sanding should work.
I would like to know if there is a similar method for finishing PLA as well like the acetone for ABS