Hardly anything is account-wide in Classic. At least in retail, you can permanently earn cosmetics and achievements, even if your gear is going to get replaced someday.
Also, combat is much faster in retail, and using a multi-target rotation is actually a thing in the open world.
I played Vanilla and all the expacs when they were current, and the only one I would play again is MoP Classic. MoP was the pinnacle of WoW design. It all went downhill after that.