The Corridor is in better shape now than it has been in years, with a few prominent exceptions.
Most of the track was rebuilt in the 1980's, and 90's.
New Haven to Boston was electrified (completed) 2001.
Metro-North has done extensive rebuilding between New York and New Haven, although the biggest job of all -- replacement of the 1890 4-track swing bridge at South Norwalk -- has yet to be undertaken (probably a four-year project).
A few major bridges between NY and DC must be rebuilt (such as the Passaic River drawbridge). Perhaps also the Susquehanna River bridge south of Philadelphia?
And as I've mentioned before, the Hudson River tunnels (2) and East River Tunnels (4) on either side of Penn Station in New York will need replacement, and soon.
This can't wait much longer. The loss of even one of the Hudson tunnels would have a devastating impact on the New York/New Jersey economies. So much so that it would make the World Trade Center attack look trivial by comparison.