Besides ease of fluid changes and looks is there a lower lube temp benefit to changing the covers?
You will likely see a lower temp, but whether or not that's a benefit depends on how you use the truck.
Years ago I spoke with an AAM engineer who stated we didn't even need to run 75w-140 unless we were running at or above GCWR thru Death Valley. That was back when the HO had 610 lb/ft and a much lower GCWR. Regardless, the axle is designed to be used as equipped up thru GCWR (which does include 75w-140 on the DRW HO's now).
I've ran a diff cover with extra cooling and extra lube capacity and the biggest thing I noticed from it was decreased fuel economy when the fluid was cold, and the fluid took a LOT of miles to warm up.
So it really does depend on use. If your loaded up to GCWR all the time, live somewhere hotter than average, and run hard then you may benefit from a potential decrease in lube temps. If you don't, then you need to analyze how you use your truck, as it's the most efficient when everything is at operating temp.
These days I just run a high quality gear lube and call it good.