Nice ideas. Mash units and contacts and stores are good. Here's a few more.
-alternate means to move around the site. Have temporary, in-zone tp bracelets issued to heroes that can tp them back to the exit, or even to specific waypoints. They take as long as regular tp to activate, so chances are they won't save your bacon in a fast & furious fight.
-portals, tucked away here and there, which tp you to different areas of the map. Set up by villains, so there's likely to be villains near, possibly on the other side of the portal.
-being largely deserted, this is a good place for villains to hide caches of weapons. Have randomly spawned temp powers here and there. The power, and the locations, will constantly change, making it a sort of treasure hunt experience.
-functioning info booths would be nice. Some people like to see who's doing the most in a zone
-doors like the halloween event, where random doors might spawn monsters, give influence, enhancements, or inspirations. Possibly even DO's or the rare SO.
-doors can sometimes open to missions that can be done without needing to go through contacts ("As you enter the derelict building you are greeted by a spatter of dust falling from the ceiling and the agonized call for help from deeper within the wreckage")
-create another faction or two for this zone. Maybe it became occupied by homeless people before the villains encroached, and they've refused to leave. This would give you a reason to have contacts and stores inside. It would also give the vahz more reason to be there other than year-old skeletons from old cemetaries.
-Possibly put a functioning tram in a heavily guarded section that is being reclaimed by military and construction. Alternately, and more likely, have a helipad with a helicopter on it that you can enter. This will transport you to one of several zones where there's a building with a helipad on it. Steel Canyon has one on ground level, so that would be a good one. It's also not far from Blyde, as I recall. Other zones have helipads I'm sure, even if only on roofs. Find ones with fire escapes leading to them and use them.