Eh, Chester's not so bad. But there's no way you'll get 18,500 soccer fans there for every game. The LA Galaxy have a 27,000-seat stadium, and they average about 19,000 fans. That's with Beckham, and a population of 10M+ (just in L.A. County). The entire Delaware Valley only has around 5M people. Also, the community is much, much more diverse here, with people from many Latino countries, as well as a large Asian and African community.
So, basically you have maybe 2M-3M (conservatively) people who are rabid for soccer, but they can't even sell out regular season games. I think the Philly Union will be a disaster. I hate to say it, but it's probably true.