I enjoyed watching that clip - nice quote by Boardman regarding the Baltimore tunnels (going back to the Civil War era). To think that tunnel opened in the late 1800s and the NEC is still dependent on it...wow.
It always bugs me when people get all wound up in how old something is. It does not matter how old it is.
What does matter is, in order of importance: The alignment, the clearances, the condition of the structure. The reason for this order of items:
If the alignment is such that high speed is impossible, the rest of the issues do not matter. It the past, there was a lot of alignment revision work, but under current financial conditions, environmental rules, and political realities, alignment is essentially forever.
If the train won't fit, the clearances can be increased, not cheaply, but not as costly as an alignment revision.
If you have alignment and clearances, then the concern is structural integrity, and for bridges adequate capacity. If the train does not fit, or if the load capacity is too low, the condition of the structure does not matter. Sturctural issues, such as conditions of the liner, water intrusion can be fixed, usually more cheaply than clearance increases. In fact, if clearances need to be increased, usually condition issues are solved as part of that process.
For specifics relating to Baltimore: No matter what they do to the tunnels, the alignment through the city as it is will always be slow. You are simply dressing up the pig. It is still a pig, no matter how much money you spend on making it look pretty. Waht is really needed to speed up things through Baltimore is a new straight alignment across the city, probably on the alignment of the Interstate highway through the city that did not happen. A four track tunnel comes to mind as a good thing.