Here's something to think about in the wake of the crash of Amtrak 188 in Philadelphia last week: Only about 4% of the rail passengers in the Northeast Corridor ride on Amtrak trains. This oddly-titled NPR article mentions that there are about 750,000 daily passengers on the NEC across 2,200 trains, but doing the math on Amtrak's annual ridership gives them only about 32,000 passengers out of that total. Everyone else is riding commuter trains.
Amtrak riders take longer trips, so the ratio of passenger-miles is probably significantly different, but won't put Amtrak in the majority.
So, while Amtrak deserves plenty of scrutiny for what they have and have not been able to achieve in the corridor, the commuter agencies also need to be considered. Have they done everything necessary to support and fund needed upgrades? Have the owners of non-Amtrak sections of track (MTA Metro-North, ConnDOT, and the state of Massachusetts) been putting in the needed effort? Have the freight operators that use segments of the line been helping at all either?
Of course, Amtrak owns most of the corridor, so they should be responsibly pricing track access and the contract operating services they provide to regional commuter services in order to fund appropriate repairs and upgrades along the route. Have they been doing that? I don't really know.
I haven't had a chance to count up all of Amtrak's trains along the NEC, but I think they only have about 80 daily on the route out of the total 2,200 (again, most trains only travel short distances). [Edit: This report from 2013 says there are 154 Amtrak trains that use the NEC daily. I think I'll have to do my own count eventually.] There's no way that they could pay for all of that upkeep solely on the profits of the Acela, Northeast Regional, and the smattering of other Amtrak-branded trains that run in the corridor.
If Amtrak was the only service in the NEC, they'd only need two tracks, but much of the corridor is four tracks wide.
All of the trains that operate on the NEC need to be dispatched in a unified way, and they need to have suitable signaling systems that all interoperate (for a discussion about this, take a look at this Let's Go LA blog post). Since the federal government remains intransigent about giving Amtrak appropriate funding, the railroad should lean more heavily on the commuter services in the corridor and the states that they serve.