Let's remember Logan, Nicetown, Tioga and Spring Garden were all dumpy stations in really bad neighborhoods in the 80s. I've seen photos during their last years of service and they looked like something out of Beruit. It's not surprising they were low ridership.
Spring Garden in the 80s was also a desolate area. Perhaps not much better today. Girard Avenue on the other hand is on a rebound. And while the subway is close by, it sure would be convenient for those who need to hit UCity, Trenton, Airport, etc, to get a one seat ride after hopping off the 15. It makes sense since it has direct cross service with a CTD route. If you're looking at CTD as competition, you're looking at it the wrong way. Regional rail is complimentary to CTD. It's a pain in the neck on east Girard trying to get a train. Hop the 15, transfer to the El or BSS, then walk to the station. It works, but when you're heading to Glenside or Langhorne, it's frustrating to have to waste 30 minutes to go into town, only to go out again a few blocks next to the path you were just on.
If SEPTA were to provide better transit connections to Temple, that would be a great alternative. Move the 3 bus over a few blocks, or start some kind of circular route that hits Front & Girard.
If Allegheny had better accommodations and service, ridership could go up. Conversely, close Allegheny where it is and build a new station slightly northeast that served both the Norristown line and Chestnut Hill line. Kill 2 birds with 1 stone.