Or (assuming the Cap is on time into Pittsburgh at the butt-crack of dawn) a transfer to the Pennsylvanian there and a pretty ride across the state, including the famous Horseshoe Curve, to NYC via Harrisburg and Philly. As you say, for a trainfan, it's the journey, not (just) the destination!
This actually seems a pretty low-risk plan to me. If the Cap is running too late to make the connection in Pittsburgh, stay on it and continue with Plan A (i.e., continue to WAS and pick up a regional). Oh, yeah, call Amtrak customer service and make sure they're on board with the revised itinerary. Literally and figuratively.