Fitting disks, fenders, and racks to a frame is a royal PITA unless the latter was carefully designed to accommodate all. Sure, disks are great. I love mine. But my touring bike was purpose-built for disks. Despite this, the real estate around my rear triangle is quite crowded.

You can improve the stopping power of your calipers by using Kool Stop brake pads. Braking won't be as good as disks or even cantis, but your braking ought to be good enough under most conditions. Just be more conservative about going downhill.