pretty much went that way as well. my favorite part of the game is healing. my first 80s were a paladin, shaman, druid and priest :-)
Then i added a warrior and now a mage.

for this second team, i thought of what i'd want it to be eventually, and for taht (instances) i needed a healer.
in the end i created 3 troll mages, and 1 troll priest. They will either join my 80 mage later on, or make use of my 80 warrior.

Along the way, i might mix them with my 58 dk or 63 lock, but i'll probably just use the mage or warrior to boost them.

Thanks for all the input !