They said that they were working on a way for the market ward item search to show you the specific materia values.

No one should be "spending millions to buy a +55 HP materia" when it's the lowest possible option from that particular type. The market will bear whatever the masses will pay, give it some time and they'll likely go down in price. Right now, I have no tier IV materia slotted because I refuse to pay those exorbitant prices. Also, if you're ripping your +55 materia out when you find a +70, perhaps you should consider buying a new version of that piece of gear and slotting the +70 as opposed to just vaporizing the materia. Yes, I realize that the current market item search doesn't support showing the different stats of gear due to materia, just like it doesn't show the different stats of materia itself, but you could easily end the price in a 1, 2, or 3 (as to indicate higher quality) to get people to come look at your pre-slotted gear.

I really don't see a problem with differing qualities of materia.