I think the DDO Store ought to sell +3 and +4 tomes as well as Past Life Tokens.
Regarding +3/4 Tomes:
Turbine has already placed +2 tomes in the store, which used to be valuable in game items. There has also been the introduction of ship buffs and countless other non DnD buffs implemented into the game. I don't think that adding the ability for players to get +1 to a given/all stat modifiers is game breaking or even game changing. There is currently a way to get these items in game so it is not going to be a case where people "have to purchase" them.
Regarding Past Lives:
Sell "Improved" True Hearts of Wood that allow players to True Reincarnate their toons using the first life experience table. Allow players to purchase one of these hearts with 50 epic dungeon tokens. Current XP requirements were poorly thought out (especially for 3rd Life + toons) and I think that this would make TRing more accesible to the masses.