I met a guy with an 84 C10 that installed one, and honestly, I just didn't like it. I usually drive around whatever truck I am currently rehabbing for 3-6 months. The one I currently am in is a 1980 GMC K15 with no factory air. No dash vents, just the kick panel pull knobs and the vent windows. You would think when I need to go to town during the humid summer dog days here in the south, I would take my late model 2500 Silverado. Nope, it stays in the pole barn. I pull those vent knobs open, and crank the side vent windows all the way out and I love it.
I am sure some folks prefer no vents, but I just have too many other things going on to add a cosmetic update to my list.
I'll only add that it may or may not affect resale, depending on how you styled the rest of the truck.