I am in a similar situation. I have 4 lvl 70 Draenei Shamans. one of them is on an account my friend setup (something I didnt know when i started, and I was more haivng fun than anything serious.)

Now I have to choose to roll another Draenei Shaman, to get 4 again, or a Shaman and a Paladin, to make it easier to do Heroics with (I have a druid and it sucks)

OR..

Reroll Horde and level 4 Troll Shamans on Mag with Zerg, or another Ruin BG for fun.

thing is, it will take about the same time to lvl a whole new set of shamans to 70, but my alliance ones are already pretty geared, some s3 s1 t4 etc etc.. With the new honored pvp gear available, arenas will be a lot quicker to gain levels, you wont be stuck at 1500 for a month because you have 0 res and so also don't make a lot of points per week etc etc

I dunno.. i want to play horde because i like them better but my mains and my money and everything is alliance.. ><