So there are two types of gamers in MMOs...
The grinder....one who does not mind repetition, but prefers to get to his/her goal as soon as possible in the most efficient manner possible. Currently DDO caters to this type of player with the current XP system especially in epic levels.
The adventurer....one who prefers to enjoy the game rather than the grind and prefers variety over the grind.
Both of these types of players TR and likely will epic TR. And most of the new players coming to this game are likely more of an adventurer type.
My suggestion when looking at the new XP curve is to leave many of the familiar grind quests (such as Deleras 2, Shadow Crypt, VoN 3 and 5, Wiz King...which are all p2p) and maybe scale up the XP on bought packs so that they are more enticing for players to buy, expecially the unpopular packs such as Restless Isles, Amrath, House C and Threnal. This wold resolve most of the issues with the grind and have more appeal to the adventurer type of player as well as promote new adventure pack purchases. Epic quests could be done in a similar fashion so that anybody interested in capping EDs doesn't have to run 1 or 2 quests until their brain turns to tapioca if they so not choose. Also challenge XP really needs to be taken up, something close to what it used to. At least 1 run could be for monster XP and successive runs could be scaled back.