If you are from out of the region and need to fly to AC on AA, I still would think the door to door time is shorter by just getting off in Philly and renting a car. it's almost exactly 1 hour from PHL airport to downtown AC by car. Maybe a little longer if you hit rush hour in the PHL area and bridge. By the time your half way there, the PHL-ACY bus will be boarding and by the time you get into downtown AC, the AC bus will be 40 minutes behind you.
Having rented vehicles from PHL and done security there a few times (I generally avoid it), I would say the ACY bus would be time/money well spent.
There are no reasonably priced gas stations very close to PHL. Last summer I exited somewhere off of the Blue Route and drove around in what ended up being a large circle until I found one.
I've also encountered the traffic jam/accident on the Blue Route while in a rental car, which resulted in missing my flight from PHL.
Overall, if you can return a vehicle to ACY or ABE, clear security there (that is a disaster on a good day at PHL), and arrive post-security, just having to make your way to a gate, then that is easily worth $50 to me.
I visit family in Northeast PA regularly, and will usually opt to fly to AVP or ABE just to avoid beginning the trip at PHL. I'll arrive at AVP and be at my gate in 15 minutes, or less. That includes parking/returning the rental car (there's a cheap gas station just the other side of I-81), checking bags, and clearing security. At PHL...on a good day that might be 30 minutes, but on a not-so-good day easily an hour to 90 minutes.