In the "Rules Forum", there's a post that's titled "Appearance points judging guidelines" by Randy Smith. The post is merely the publishing of a PAMPA document, not Randy's creation. It was drafted by all the PAMPA Officers and District Directors. It has the answers you seek, about matte/gloss.
You have to ask to be allowed to join that forum, and provide your name and AMA or SMAE number, etc. The permission will also allow you to read and post on the Judging Clinic Forum. You have to contact Sparky, tho I suspect Randy Smith or Bill Little can give you the permission. I am a moderator, but I can't do it.
I have a problem with this document, because it's a PAMPA document, instructing the NATS judges how to do AP judging. It's not in the rulebook, which means to me that they are not running the NATS (of all contests!) by the rulebook.
It doesn't allow judges to downgrade a model that's ugly, or upgrade one that's handsome. It doesn't allow judges to downgrade a model for having an ugly color combination, or reward one that has a good color combination. It doesn't allow judges to downgrade a model for having ugly graphics or reward one for having an artistic graphics design. Basically, it allows an ugly model with crappy colors and dopey graphics to get 20 points, and I have difficulty with that.
The rulebook simply says "appearance", and to me, that includes shapes, colors, graphics, smoothness, ink lines, cockpit details...the whole enchilada. Thankfully, the "Pilot's Choice" system of determining the Concours Champ seems to work just fine. Folks know a good looking plane when they see it, such as Bruce's Jester.
Gloss or matte should be as appropriate, by either PAMPA's document or the rulebook. The year that Ron Burns got hosed by the judges, I believe the AP judging was done by a team of R/C pylon racers. However, PW told me at the end of the B-17 project, that the gloss finish (B-17 #2) was because the matte finish (#1) was heavier.
Steve