I can't answer your question about riding from the airport, but I'll second the notion that it's in no-man's-land and that Septa rail is an easy ride from their to center city.

When I ride the Schuylkill River Trail, I start at the Art Museum and ride the roads around the unpaved area. It is easy to do that and I find it more enjoyable on skinny tires than the unfinished part of the path.

I think Philly has become much more bike friendly in the past few years. There are many more bike lanes than there were, and I feel like there are more cyclists also. And it has great food