From time to time I have been running all my shaman as resto.

It's slower to kill, but it's much safer - so less deaths and no down time (so it is faster moving from mob to mob), and they never have mana issues spamming lightning bolt.

4 x riptide, 4 x imp heal stream totems and earthshield on the tank make him robust to not usually both with actual heals. However I use the quick heal x 4 if he ever needs a top up - doesn't affect mana much as it goes back up shortly after.

I used this setup to kill Onyxia as I was running out of mana with Ele spec.

I've used it in Grim Batol, Halls of Origination etc.. (unfortunately still need ilvl for heroics) and it makes things quite calm - no panic ! I had to switch back to Ele for bosses that needed to go down much quicker though.