All this is my opinion and you can tell me to suck it if you like. Half of the cars/trucks I build I do rear conversions, but only if it adds up.
Other than wet environment there is almost no benefit on the rear.
Pros:
Easier to change pads then drums
Possible braking improvement but since your rears do about 30-40% of the braking and unless you are upgrading to a 14" rotor and 4-6 piston $3k rear set-up, you'll only get a maybe a 10-20% over a drum, the net return will be maybe, maybe 3-5% better. Only in the right environment. If you tow, you'll overheat a small pad much quicker than a large shoe.
Cons:
Ineffective parking brake on most set-ups.
Rear disc suffers from knock back issues unless it's a full float. Have to drag or pump brakes to keep pad to disc if road racing.
Reduced gas mileage. Disc brakes usually outweigh drums when you add up bracket, calliper, rotor. Increased unsprung weight and more rolling resistance as pads frequently in contact.
Increased lining changes. How often you change shoes vs. Pads? I would bet 2-3x as much.
Racing-yes
Off-road only-yes
Rain every day and you don't know how to pump-yes
Daily driver-no
If it's a 1/2 ton. Better return is the larger 1/2 ton drum set-up. Increased performance without all the hassle. Cost $50-100 at junkyard and another $100 for all new parts for it.
