Finally pulled the trigger on a motor kit and battery. I bought
this 48v 1000w kit off ebay. It costs a little more than their cheapest kit, but it comes with a half-twist throttle instead of a thumb throttle and has a speedometer (we'll see how good it ends up being). Should be here by the end of the week. For the battery, I went with a 48v 15Ah LiFePO4 from Ping. I should get it in a few weeks.
Got the new tires and thorn resistant tubes (no Slime) put on. They're much quieter than the knobbies, but I can't really tell how they compare for rolling resistance. My commutes seem a little easier, but that could easily be attributed to me getting used to it. I've ridden to work a few times with them and no thorns or leaks so far.
I'm still considering getting another bike. Mine is a little tall for me, but about perfect for my wife, who wants a bike. So I could give her mine and I could get another that is a little smaller and has disc brakes. Going to go to a bike shop or two today and see what they have. I would like to go with used, but Craigslist seems to be my only option here. Hopefully these shops will have some used bikes that will work.