I find that mobs go down so fast that flame shock isn't really viable until 75 (with lava burst). I'd go with:

/castsequence lightning bolt, chain lightning, lightning bolt

or

/castrandom lightning bolt, chain lightning, chain lightning, chain lightning

As for the instance, the only thing you have to worry about is gold. The rep you can gain is fairly useless when WotLK hits. I'd go with underbog up to and including the first boss (then exit, reset, repeat) which is nice xp and more importantly herbs, ore and shards (assuming you have your gathering professions up to date). When you reach level 66/67, go sethekk halls and stay there until 70, where you should be exalted with Lower city for a nice trinket and epic main hand spelldmg weapon :-)