My experience has been that leveling elemental has not been nearly as tedious on mana as people make it seem, perhaps we are all spoiled from our never ending supplies of mana and health when we reach raiding status at 70. I remember leveling my warrior, and my original shaman (Enhancement) mana, and eating for health as the warrior, were far greater issues then mana with 5 shamans. I personally was able to blaze through levels after about 20 without even trying. Once I started running ZF I could do about 6 pulls without drinking, just by making sure to use my totems effectively (Pull back to a totem farm, rather then move the totem farm every two pulls). This also reduced the risk of pulling more then desired, further decreasing my downtime, as I didn't have as many mistakes.

I went ahead and specced somewhat an end game raiding spec, with a few twists and turns (And a misclick.. grr). I of course have played a Elemental shaman since TBC came out, so for me it was a very easy transition, with no learning curve to play 5.

I'd imagine Enhancement would be less mana intensive, but I doubt it would be as powerful for soloing instances (Which may not be an issue for you if you don't plan on instancing). I also know that on non elite trash during quests, I almost -never- drink though. Once every 3 or 4 minutes maybe, but generally things drop in one bolt of lightning, and an earth shock, and I regenerate enough to keep mana up. I do however wear spell caster gear, mostly cloth, which can be bothersome.

If you do go Elemental, talents that are almost a must for ease of leveling are Earth's Grasp, and Improved Fire Totems. The decreased time on my fire nova make it amazing in large pulls. Pull with a single lightning bolt, drop 5 Stoneclaw, wait 1 second, drop 5 fire nova, move backwards, Chain lightning, and then start bolting it down. You can probally skip the +hit talents (especially if your a Draenei), or at the very least drop them at 50.