I *am* a little torn just because my road bike is new to me, gorgeous and so fun to ride. I'm thinking why ignore it and go back to my oldie but goodie? But you're right, I don't want to stick it on a bus rack if I don't have to, much less lock it up outside my building. I don't carry a lot to work either so maybe a messenger bag would be enough. I probably won't ride in rain/snow at least for now. I won't be frustrated going slower. So...my current mountain bike set-up is probably decent if I swap out the tires and add lights.

This is really helpful, thanks everyone!