If I understand you, you believe that the items are priced correctly so unique abilities come with a steep price. Well that is the system we have now and it seems people don't like it. I'm not going to pretend I know enough to balance every item in the game to make everyone happy or to even balance it. What I'm suggesting is an automatic balancer based on the law of supply and demand. Once the items become priced correctly, then all the items are getting used and we see NEW statagies.
I'm not even sold completely on my own argument, but what is the point of having items that no-one ever uses? This thread is titled 'Equipment Balance Overview' If we follow your logic, everything is already okay and there is no need for any more balancing.
I'm much more decrying the market approach here than defending the current balance of many of these items.
Look at Rook, for example. Structural transfer is just awful and towers are ridiculously good. Logically towers would have been buffed and structural transfer would have been nerfed, because in spite of their true effectiveness the game would have rebalanced them off of popularity. The result would have been that towers, which already do batshit insane damage, would have been buffed until they were overpowered to make them popular, and structural transfer, a crummy ability, would have been made even worse.
Also a lot of things just aren't popular because people don't like them. The guys at Blizzard were actually very cleverly aware of this. In the WotLK beta they would add a new ability that sucked or was broken and of course it would get next to no usage. When they were ready to get that ability into shape they would actually overpower it on purpose so it became popular and people would test it, and then work backwards with a nerf.
In DG terms if you tried to make QoT popular after being weak for so long you would almost definitely have to overpower her to spark interest and then nerf her back into a place moderately better than she was before you changed anything at all. That's fine in a beta but it's not a viable approach after launch.
Now I realize you're talking about items and not abilties, but I don't see why the same logic wouldn't be applied to overall game balance if it were implemented for items.
So again an item with crummy stats and a goofy proc would have to become extremely cheap to make it worthwhile because of its awful stats. If it became cheap enough to become common that goofy proc would be useless the majority of the time, but it could potentially be devestating to a specific Sedna and Erebus build.
I'm not defending the hat here or even its current price. What I'm saying is that if its price were the only thing you tweaked until the item became as popular as say nimoth's armor, you would have to reduce its price to an absurdly low level and effectively make what is currently an effect which fills a tiny niche into a basic effect most DGs have in common which arbitrarily punishes any regen build.