This is exactly how I feel. A lot of the time people focus on the challenge of the numbers game and balancing out powers, but the numbers game in PvE content was won by players a very long time ago. Balancing out powers at this point is just comparing efficiency of winning, rather than the difference between victory and defeat. Doing something to enemy values is, as you say, just an illusion of difficulty that only draws out battles for longer or might require some shifting of numbers on the player side.
I'm also not keen on difficulty that makes the grind longer. That isn't real difficulty, it's just... longer. Pooling salvage in the AH is a very welcome change.
It's a tall order, but I'd love to see more strategy brought into the game, like the LGTF Hamidon fight. Boss fights that require you to be in the right position to avoid AoEs or that requires some team coordination would be really enjoyable to me. While breaking the usual MMO tank/healer/dps pattern should be hugely celebrated in the game, I would like to see content that does need damage to be soaked directionally or that puts healing powers back in the picture. Some of the new content had fun stuff like this going on, but I get the feeling it was really hacked into place from the limitation of the tools.
I self impose a lot of challenges, as others have suggested. On that account, I get very bothered when one rogue member of the team decides to go off and speed run the mission just because they can. That, more than anything, has really taken the fun away from the game for me over the last few weeks.