For me personally, I would want to lose the grip shifters and change to trigger-type shifters, put on smooth tires, and switch to a rigid steel fork (US$50 from Nashbar).

Check out the thread I started about my old MTB back when I first joined in 2012, and how I changed it over the years to better suit my road riding style/needs.

http://www.bikeforums.net/hybrid-bic...-friendly.html