I'm not a huge fan of the gray. However, it's definitely better than full black, at least. How much it seems to crowd the other colors seems to depend on zoom - I feel like I can see the interstates, US routes, etc. better in the existing color when viewing the whole of NY, for example.
One idea I don't think we've considered is taking a page from Australia and using gold for the primary state routes and light salmon for the secondary systems, with usanp, usaush, and usatxre retaining brown.
Here is what it looks like.
Personally, my top choice remains using the dark green for usanp, usaush, and usatxre with brown retained for state routes, but making the display more like Australia as detailed above would be my second choice. In any case, a large-scale change should also have coordination with the systems in development in Mexico and elsewhere that use the US/Canada color scheme, and perhaps also a revisit of how things are handled elsewhere in the world (especially as Europe and Australia are basically opposites for gold/light salmon usage).