Thanks for the help, everyone - this is really good advice. First, I do all my repairs myself - I really like the feeling of riding a bike that I've put a huge amount of myself into. On my current bike, I've replaced the cassette, redone all the cabling, trued the wheels somewhat, and replaced the front derailleur.

About handlebars, I had a close shave with an SUV the other day that has made me significantly more concerned about safety (duh). I was coming down onto the Boston side of the Harvard Bridge with significant speed, and was a little too focused on the pavement because it's really bad there. My light was green and it was broad daylight, but the car still turned left onto Beacon St across my path. I didn't hit the car (or get hit), but my bike did flip. I'm luckily totally fine, but I've been thinking maybe this means I should have bigger tires - specifically for that intersection, which I go through 4 or 6 times a day usually. There are other dangerous things there too - taxis do some really stupid things, for example.

Maybe I should get something with upright handlebars and then add drop bar ends. Are those useful at all? That way I can go into the drops when facing a headwind (which are usually pretty strong going across the aforementioned bridge).