i could go on and on, but haven't the time
check out world.nycsubway.org they have great trip ideas. 30th street is a good spot, but since all the equipment is pretty much the same, go to north philadelphia- freight, NJT, Amtrak, and two SEPTA lines diverging into two different stations on spot.
most worthwhile subway/trolley rides are in my mind routes 100 and 101, and the MFL. explore 69th street terminal.
the broad-ridge spur is VERY depressing and run down- ride the BSL near fern rock, where you'll get better pics and more interesting loop rides and yard pics.
look in suburban station where you can get one of the best looks at the push-pulls.
as for regional rail rides... most of them are pretty generic. i recommend the R5 paoli etc. ride as far as you can go. can take amtrak keystone back, which is a fun combo.
TOP HOTSPOTS: North Philly, 69th street, fern rock, and whole suburban station complex
know you can't do all this, but these are all worthwhile.