Spell damage is pretty important to a prot pally.

Sort of varies on what your doing though.

Like a hyjal prot pally needs a crapload of spell damage to make it easy. Our prot pally had like 600 and we would often give him WoAir.

If your only boxing 5 mans with a team of 5 I would suggest to do whatever feels right to you. If you find yourself getting caught by your slaves I suggest getting more however stam/skill def is important too.