I have to strongly disagree,
First JFK has 2 brand new terminals that are really nice (terminal 1 & 4), plus another monster terminal being built to replace AA's 8 & 9. The roadways have been totally rebuilt, new ATC tower, and excellent runway set up. Terminal 7 although a mess now is going to look great when renovations are complete, Jet Blue has terminal 6 busier than it ever has been, and DL's terminal 3 is not that bad considering it's age.
Also JFK's $3 Billion+ Airtrain is opening it's first segement this fall, the inter terminal area and the link to the parking lots and "A" train at Howard Beach. In 2003 it will be operating between Jamaica station and JFK, eventually there will be a one seat ride between NYC and JFK via the Van Wyck row. However this will not be feasible until the LIRR's East Side access project is complete thus opening enough slots at Penn (and or Grand Central) to allow the JFK Air trains to operate to Manhattan.
With regards to LGA, it serves it's purpose well. That is it's a close in regional airport, it's not meant to be anything but a regional airport. Boston, Chicago, Atlanta, Florida, Toronto, Montreal etc..
I think the Port Authority has done an excellent job renovating the main terminal building at LGA, yes it's cramped in the concourses but the core of the building has had it's usefull life extended 30 years with the renovation.
The Marine Air terminal serves it's purpose well and is a nice retro piece of NY aviation history, the US Airways terminal is still amazing 10 years after it opened, the DL terminal is in sorry shape and does need to be replaced or get a serious renovation. But that's DL terminal, and they would rather rebuild Terminal A in BOS then renovate their LGA terminal.
Also eventually the Port Authority and the MTA will extend the N train to LGA, offering an air-rail connection similar to DCA's wildly popular Metro station. 30%-35% of all DCA travellers travel to the Airport via the Metro.
EWR is under going a major renovation too, Continental's Terminal C is really nice. They have extended the usefull life of that terminal, and it's one of NY's best. Terminal B at EWR is undergoing renovation as well, Terminal B has one of the nicest IAB/ FIS halls anywhere. Terminal A will be getting a renovation similar to Terminal B's in the next couple years.
Newark also has a new control tower opening this Spring as well as Air Train which has been operating for a year now, eventually the PA will extend the PATH directly into the Terminal area offering one seat rides to the new WTC.
With regards to capacity the FAA is redrawing the air routes around NYC which should help relieve congestion at all three airports, JFK has a good runway setup. There's no need to add runways at JFK, LGA is a small close-in regional airport. There's no way they would add another runway because all that would do is draw more traffic away from JFK, LGA hurts JFK. Because airlines put all their domestic flights into EWR and LGA leaving JFK as a international gateway rather than a hub.
Newark could use another runway, it's the busiest of the three NY airports and has a poor runway set-up. It has two parrell runways that are too close to allow for simaltaneous arrivals/departures, and it's cross wind runway intersects the two main parrell runways meaning aircraft must wait for traffic to clear before using the runway. Newark is surrounded by the Port of Newark/Elizabeth on one side and a huge area of vacant warehouses along it's Western border.
Newark has the best chance of getting a new runway.
As for new airports if you want to read a good book check out "Empire on the Hudson", a little known fact was that the Port Authority was looking for a long time at building a 4th passenger airport in the Great Swamp in Morris County NJ.
Eastern Air lines flt # 701, EWR-MCO Boeing 757