Ok, some more info.

I just looked at Ellay's proposed end game PvE spec which made me look at the Enhancement tree a little more carefully.

With your suggested spec you get the following out of the Resto tree:
25% less mana for totems
5% less mana for healing
reincarnation bonus
70% less pushback on healing
5% crit to healing and lightning spells

For a total of 20 points.

Enhancement:
10% extra intellect
5% crit to everything
45% less mana for shocks

For a total of 11 points.

So just from a mana efficiency point of view while leveling up, especially grinding through an instance, I am thinking of 11 points into Enhancement and 5 points into resto and then I start down the Elemental tree. I am not too concerned about being ganked as 5 shaman have a lot of firepower, players have to significantly outnumber or significantly outlevel me to pose a threat. I fancy myself against equal numbers and levels as well, they don't have the coordination and focus we have, they probably don't have the firepower and you will have equal or better gear if you farm instances as well. If you are targeted by a few 80s you will probably lose anyway and the times a few more points into elemental would have saved you is too situational to base a spec on.

On the other hand, you can buy dual spec and try out both once you've got enough cash. A thunderstorm build for PvP, BGs, dailies etc, and a mana conservative build to level/grind with.