I sat through a briefing last fall by the museum curator. The vehicles are undergoing restoration. I believe it cost something to the tune of $35-40,000 a vehicle to restore. Besides money, there are some environmental issues and water usage (only so many thousands of gallons of water that the recycle tanks can hold at a time, many HAZMATs in the paint, like lead and old POL products).
The old paint schemes were applied only to slow down the deterioration process. Many modelers complained that the old colors were not accurate, and they were right. But it kept the vehicles in one piece until the money was available to do t right.
Currently, they are doing a beautiful job in restoring and repainting the vehicles in accurate markings. The vehicles do have a gloss finish, but that's just to make the tanks more weather-resistant.
APG no longer has the famous "mile of tanks". This was a strip along one of the main roads where many tanks were displayed in the grass median in between the inbound and outbound lanes. Apparently a woman went off the road and hit one of the tanks in her car. She sued (don't know the outcome) so the post removed the tanks from that area.
Many tanks are at a warehouse near the ordnance school awaiting restoration. A few have been placed at various locations throughout the post. Several are on the south side of the road where the mile of tanks were. Bad news to scattering the tanks around the post is that non-military folks are only being allowed to visit the museum and not able to wander the post to see all the newly restored vehicles.
Since Aberdeen was where many vehicles were tested and developed, there are plenty of "one ofs" and prototypes not found anywhere else. Down side to this is that many of their vehicles are prototypes and not production models. Also many captured vehicles that were evaluated in the states are located at APG.