That is a great rate for ABE to TPA in late November. I would take that and keep it.
I have flown US AIR from PHL to MCO 3 times, BWI to MCO 1 time. I have never had a problem. In fact, I flew once when my son got sick to his stomach and had the nicest flight attendant on earth. I would never hesistate to fly them.
The problem in PHL is the airport, not necessarily US Air. BWI is far better in comparison, but further for a lot of people in PA/DE region.
ABE is further from Fort Washington than PHL, but not much. It is a quick ride up the NE Extension (50 - 60 minutes - probably less). If I lived in Fort Washington, I would not hesitate to take a flight out of ABE. I have heard nothing bad about that airport.
I live in Delaware and I would fly out of ABE for the right price and it's atleast 2 hours from my house.