As much as I hate the Yankees, I'll use the example that A-Rod was a solid performer with gold glove all-star/hall of fame numbers that was a can't miss for any team that signed him. At the same salary, Derek Jeter can be a defensive liability who puts it solid, not spectacular numbers. The Yankees are overpaying for A-Rod, and have a steal with Jeter.
So when Joe Freehold spends his money at the Bears game, or Tammy Linden takes her family to the museum and then for a bite at the Brasilia Grill, the're not only contributing directly to the general revenue of Newark, but they're also going to tell their friends what a great time they had, what great food there is, and how they'd come back. Without the light rail, I don't think those people would be so brazen to have stepped foot outside of Penn Station.
The Star Ledger had a great writeup that pointed out all of the highlights in the city: