It's not the antenna itself that may have come loose, but the separate 12-volt power lead that runs along most of the length of antenna cable to supply power to the amplified base. If you've been having reception issues for some time then it's likely you have a pre-existing condition. Check the power lead and fuse. If they both check out then you've likely got a faulty antenna base which is relatively simple and inexpensive to replace.

As for the idea of committing the monthly expense to a "second car", consider a portable satellite receiver. My wife and I both have Sirius S50 units and move them freely between multiple vehicles, docks for use in the home and office, and since they're also MP3 players (and have TiVo-like capabilities) use them for stuff like cycling and the gym. It's nice to actually be able to record something you like on satellite for later listening just by pressing a button. So the monthly fee covers a wonderful device that follows us around where we want the music rather than having to go to where it's installed.