I started commuting with my Alu/Carbon road bike recently. All I did was to put fatter tires that would fit within the frame and brakes. Also added P-clips as my roadie doesn't come with braze-ons. Works well so far.
For wet days, I ride my hardtail mtb with discs. It makes me appreciate my roadie more especially on climbs.
If your commute is on stretches of tarmac, the road bike is the weapon of choice.