Dont know about that but if I had to guess I would think they will not come twice as fast. A lot of your AA xp will be on discovering new areas all over the game, some blue quests. killing some blue or higher named mobs for the first time, etc. Once you hit lvl 70, your xp converts to AA xp as well.
The added AAs gives the vets something to work towards as the level cap did not increase with the EOF expansion. Whiel we also have a few new raid and group zones to check out, this is a nice incentive for us who have already reached the level cap and were twiddling our thumbs for a bit.
So for someone newer to the game and not yet having reached 70, I think you have time before you need to fully think about getting the EOF expansion. Unless of course, you are from EQ1 and want to really see Faydwer again =)