Should NJ help pay for facilities in New York City and Philadelphia? Yes, if they have perceived benefits from the location of the stadium and/or other related benefits (hotels, airport, employment opportunities, etc.).
I know I am in the minority on this, but I think construction of multi use facilities, owned by the city/county/state or what ever other government entity, supplies a benefit to the local residents which cannot be fully measured. Other similar government owned buildings are:
Museums, Opera houses/Music Centers, Zoo's, Airports, Harbor facilities.
All of the above serve to allow private businesses to function with assistance from the government. Some call it socialist, but that is a huge stretch of the word, IMHO.
DC already DOES enjoy the free-admission Smithsonian and zoo and many other amenities paid for by the whole nation.
The three major airports around but not in DC are a joint DC/MD/VA concern, as is the Metro (public transit).
Funding for operation and replacement of the Wilson Bridge is especially convoluted. This is the bridge that carries I-95, the primary N-S interstate on the East Coast, and DC, MD, VA, and the Feds all have a piece of the action.
But are you proposing VA and MD (and perhaps WV, depending on the definition of “DC metropolitan area”) pay for a stadium over which they had and currently have absolutely no control?
This is especially ironic in that DC license plates claim THEY are the ones being taxed without representation.