I've decided that having the USB onboard was worth it since SparkFun's Arduino Pro Micro is the exact same size as the Arduino Pro Mini I originally purchased. For an extra $10 I get these possibilities:
Build in a LiPo charger
Expose SD card via USB Mass Storage Device (no need to remove the card!)
Flash new firmware without an FTDI cable
Add to that the fact that the I2C pins on the Pro Micro are on the edge connector rather than off-grid as was the Pro Mini. This all makes the Pro Micro the better choice.
I have also switched to a far cheaper option for connecting an SD card. I'm now using the simple MicroSD breakout board from SparkFun.
Finally, in order to make it easier to find time to do my Arduino hacking, I bought a tiny tackle box to fit my breadboard. It came from Michael's (a craft store in Georgia) but I believe it to be exactly like this one. Now I can safely toss it in a backpack and hack code on it in my spare time without having to drag it out. Just pull the USB cable out and make the most of that bus ride.
In order to get the bread board to fit I did have to cut 1/4" off each side with my miter saw. Any time you are sawing plastic (especially PVC pipe) go very slowly as it tends to crack, then snag, then bind, then explode into shards.