Personally, I had a similar thought a year ago when I was starting out on B1,
Letsee if I can dig it up...
Here is what I've got so far:
Adv Power Plant - Reduces prices by 10% - 15%, Keeps Base Defenses active
Crane- Auto Repairs buildings (1% basewide per 4 seconds)
I want to say Garage, but I'd be delving into RA Territory and I doubt it would happen anyways.
Let me know what you think? I think it would be fun to hear your thoughts.
Rock