The cramped bike is the MTB. The skinny tire one is fine. Its low gear isn't too low, so hills are harder than they should be. Even if I get a new bike, I'll be keeping it in part due to sentimentality, but also cause its faults are few and I like it.
I went to the nearby lbs that sells bikes by Giant, Haro, and Fuji, among others. I asked one of the sales staff what I was looking for, and they said, in all honesty, that such a bike as that might not exist. So, I decided to get a closer look at what they did have. They had a decent number of Fuji and Giant commuter bikes, as well as some of the Electra line. Some of them look like great bikes. But they're not quite what I'm looking for.
One of the co-owners saw us checking out the commuters and asked if we were finding what we were looking for. I repeated my earlier conversation, and he said that an exact bike might not exist, but we could come close by making changes to existing bikes. He remembered that I had once looked at a Haro Flightline Sport. He said we could take the bike hardware as-is, put skinny tires on its existing rims, change the stem and handlebars, and we'd have a durable disc brake commuter bike with a lockout front suspension. For the price of tubes and tires, I could swap tires to knobbies if I wanted to ride trails. He said he has a bike like that at home, and took it on a long ride from Chattanooga to Panama City, FL with very good results. He'd be willing to swap the parts at no extra charge, and both colors of bike would be available next week.
Like many solutions, it's a compromise. But it doesn't seem like a bad one. Sticker price on the bike is around $440, so I have to decide if I can spend the money, and also if I really want to. It is an exciting thought, though.