Are slick tires worth it for commuting?
Yes, definitely -- if you're riding on mostly paved roads, switch to bald-ish tires. Rolling resistance is huge and equates directly to effort, though as you start going really fast it is dwarfed by air and gravity of course. Per the graph here:



However, one caution: road tires tend to be skinny, and you probably want fat-but-bald tires instead. If you go from a 35mm wide treaded tire to a 25mm bald tire, you will feel a lot more bumps.

So in summary: bald, for sure, but don't sacrifice too much width/comfort in the process.