or, is it really because eBay is a more complete marketplace now, with better information, in many ways it is more efficient, and arbitrage opportunities are lower, and market pricing prevails more often. But...it almost seems like less efficient markets are more fun to play in.

This may be a stupid comparison, but a microcosm of this might be the experience of the World of Warcraft Auction House vs the Diablo 3 one. In WoW, the market rates differed hugely by server (realm), and were influenced by drop rate, population, and relative maturity of the realm (e.g. mostly low-level or mostly high level). In short, the pricing mechanics were simple, and the supply was constrained and grokkable. It was also only fake money (aside from the gold farming, which wasn't sanctioned).

BUT, in D3, the drop rates were more random, the population on the AH was giant relative to WoW, and people were playing with real money. As a result, the market got efficient quickly, and the the pricing adjusted very quickly such that it was no fun to play. the drop rates were so low for items that of high enough quality that it wasn't worth participating as a buyer or seller unless you were only in it for the money.

That's simply not true.

There is so much more available on eBay now. I do almost all of my shopping on eBay because it presents a consistent user interface, with a quick checkout flow, and good competition between vendors to keep the prices down.