It's hard to argue with the old mountain bike advice, but I'm going to try.
I gave the rigid mountain bike thing a go with a 1989 Specialized RockHopper built up like this:
It was a decent bike, perfectly fine for commuting. I think I've got 26x1.75 tires on it in this picture. It would fit much over 26x2, but you don't need that for commuting. The problem, to the extent that there was a problem, was that I actually wanted a road bike, not a mountain bike, and even when you put drop bars on a mountain bike the geometry isn't road bike geometry.
I'd counter that what you actually want is some kind of sport touring bike. I think I saw a nice Miyata 310 on Seatle CL. There are many other options. It sounds like you have your preferences dialed in pretty well. I bet if you stop by Bike Works they'd have something that fit your needs.
Here's my 1982 Specialized Sequoia as an example of a sport touring bike built kind of like you seem to want.
