This isn't meant to be a QQ post, although I know it will be percieved as such. But irregardless I will say it anyways. I was running through farming act 1 today when it hit me, I got what I would consider to be a good item for someone. I believe it was a pair of bracer with str, vit, fire resist, and resist all. Not an overly large amount of any of them but still enough that someone should find them to be an upgrade. Finished my run and went to the ah to look for similar items.
Thats when it hit me, tons of items with similar or better stats posted for under 20k gold. I realized that the issue is not with any system in the game, readily availability of the auction house, loot dropping at a low or high rate, there being a more efficient way to farm or not. The issue is that the game is too popular. There are simply too many people connected to the same systems so as an individual it feels impossible to feel special. Short of getting the absolute best item in the game there will always be a bunch more of similar items setting a market and generally it will be less than what you expect.
At this point in the game most people who want to be in inferno are at the very least in act 1 with moderate to decent gear. So items that you find that you think man that would have been nice to have when I first got to inferno! I payed x amount for these, i should be able to sell them to some other player at that point and they will be happy to have it. But then seeing that no, its not worth anywhere near what it was before, and then looking at anything thats an upgrade for you costing an insane amount that you can't even fathom getting too, especially with all the nerfs to finding gold and the increase in repair bills.
As for a proposed solution I really can't think of one short of splitting people up into smaller clusters, which wouldn't even be an option with how many people are playing with friends from all over the country and the world. I still enjoy the game, but it just doesn't have that same feeling that diablo 2 had with the trading going on and the lack of connection systems in place.
TL;DR with how many people are playing the game it just gets harder and harder to feel like you're accomplishing anything.