Worth noting -- the ridership for the Cardinal is mostly
I think the folks in Virginia and West Virginia will throw a major tantrum if anyone tries to divert the Cardinal away from them,
* Chicago - everywhere as far as Charlottesville
* Charlottesville - NY/DC
Charlottesville is arguably the strongest city for the Cardinal, and the online traffic between there and Chicago is strong. You don't want to divert it.
Is Charlottesville Philadelphia? I would think CHI-PHL would be way more important than CHI-Charlottesville (plus, they can always take a train to WAS and connect with the CL and it might be close to if not faster than the Cardinal).
PHL is the 3rd busiest Amtrak station. HAR and Lancaster are in the top 25. No city in VA is in the top 25 unless you count DC. And West Virginia? Does anyone outside of West Virginia care about West Virginia?
There's also a lot more trains to take from PHL, and even HAR and Lancaster have fairly frequent service, a lot of which is commuter or "extended commuter" service. It's not necessarily true that those same people would use Amtrak for a long-distance or overnight service to Chicago.
The same argument that you're making for Charlottesville could be made for PHL as well - just take one of the numerous regionals down to WAS and get on the Capitol Limited. Or take the Pennsylvanian and have a few hours to relax in Pittsburgh before going on to Chicago. In fact, this argument can be made for every single city on a proposed restored Broadway Limited route. This cannot be said for every community on the Cardinal route; in fact, everyone between IND and Charlottesville has to either drive to another station that does have daily service or hope that the schedule lines up for their trip.
I'm not sold that there's a big enough market in CHI - PHL to create a second daily train that could be closely mirrored by having some through cars on the Pennsylvanian. I'd much rather see money and political capital spent by having through cars on the Pennsylvanian (thus allowing a one-seat ride for customers) and making the Cardinal daily (improving an already known strong market for long distance travelers, adding an additional daily frequency for the extended commuter service form Charlottesville to NYC, and creating further connections by having daily service to WV, VA, and KY communities that are not already served by a daily train.