Why, Why, Why would you get an airline credit card to an airline you rarely fly (let alone, you rarely fly in general)?

Unless you spend over $25,000 a year on your credit card, dont waste your time with this card. Airline cards are only good under the following conditions:
1. You fly a lot (at least ten times per year)
2. You fly an airline that has lots of destinations with opportunties for "low tiered" awards often.
Airline cards are generally the worst value for credit card points unless there's tangible benefits you will use often. Not only that, but out of all the cards, Virgin America is the most worthless. They dont fly many routes, often their flights are sold out and their redemption value is one of the worst. I'd also suggest highly avoiding Virgin America if at all possible. While they look "cool", when things go wrong, they cant recover like the Deltas, US Airways, or the United's of the world since they dont have extra planes, nor do they have 100's of flights that you can connect to in order to get back home to PHL.
I suggest, instead, if you're looking at getting a credit card, that you look at Citibank's Thank You Preferred card. You earn 1 point per $1 spent, and you can use that to redeem gift cards at major stores (Target, Wal-Mart, etc...) at a value of 0.01 per point. You can even use it to redeem flights on ANY carrier, again, at a conversion rate of 0.01 per point (i.e. 25,000 points would equal a $250 flight, which is typically what the average flight costs these days).
If you're deadset on an airline card - look to Delta's Amex or United's Chase Visa/MC. Both of theirs have generous bonus offers to sign up (normally 30,000 to 40,000 miles), and they offer free baggage...two things that the Virgin America card does not offer. Since PHL is a UsAirways hub, United's card is probably better since they are both in the Star Alliance.
Good luck on whatever choice you make! It can get confusing!