88-92 microns is really low to begin with; I've actually never seen an E9* M3 w/ that low of a clear coat depth. Every single M3 I've worked on is around 120-130 microns across the entire car, w/ 100 being the lowest in some spots. What type of paint depth gauge was he using and was it calibrated properly?
Removing orange peel is worth it if done properly. My previous car after wet sanding:
http://www.eclipsisna.com/?ena=eclipsism3-page5