I don’t have any heroic armor.
However, going from regular armor to epic armor increased my enchantment level and added a gem slot. So, I’d assume that heroic would follow suit and increase the amount you can enchant the armor and unlock the last gem slot.
As for the cost, yeah, at lvl 80 it’s 14,700 diamonds per armor piece so I won’t be doing that upgrade anytime soon lol.
Gathering materials also takes a lot time.