I completely agree. It would give some spark back to some older, and newer players alike for the old stuff that doesn't seem to even be remembered anymore. The earlier instances were very fun, had good feel and atmosphere to them. Back when, for example, Kalin Shrine or even Cyclops Stronghold were the best of the best, they were great fun!
I really think it would be a treat for us to re-live some of our old memories from when we were newbies, in the current set of the game as far as gear and levels go. Sure, we could always make yet another alt and run through them like that and blah blah. But when you ran those instances back then, you barely had ANY of your character truly unlocked. Barely scratching the surface of the game and depth your character could become and really let loose in full on boss fights, etc. Revamping the old instances to challenge the later game geared players for some fun, maybe some newer loot, whatever have you, would bring back a lot of fun in my opinion, instead of peat and repeating the same last instance over and over.