I agree so much.
Along with that, how about an NPC in every zone that allows you to adjust the level scaling beyond 60? (kinda like the lady that lets you see old Undercity).
Maybe this NPC is not unlocked until you’ve reached max level in the current expansion’s content.
This way you can choose to level alts ANYWHERE you want. Of course that comes at the price of not collecting the latest mats, but it would make the entire map a LOT more relevant.
I have the feeling that such an undertaking -upgrading the graphics and “art” in all the old zones- is simply too daunting of a task though, with not enough payoff for Blizzard. We can dream.