I can understand that after you've leveled a few 70's up, you might get bored with the old world content to some degree. After my fourth 70 I was bound and determined that none of my under 60 prospects were going to set foot in Stranglethorn Vale again because I'm sick of the place (they all did, because while I'm sick of the place, I also know where all the quests are - I can go through STV like a steam powered quest thresher now, be it Horde or Alliance quests - expediency trumps all, I guess) but I still have a hard time imagining actually giving someone else access to my account, especially someone who is in all likelihood working for a gold seller.
I suppose it's only different from playing your wife's toon while she's at work by degree, but it seems different to me. (Hey, she really wants that Firefly, it would be a great anniversary present.) I play WoW because, well, I like the game. If I disliked playing the game so much that I felt like I needed to hire someone to play it for me, I don't think I'd play it at all. Is it that important to get to 70 super-fast? Is the game so much more fun at max level that you'd actually pay someone to get you there?