Buffs in classic are much more impactful for melee than for casters. There are multiple debuffs that reduce the enemies armor (sunder, FF, various weapon procs) and attack power/stat buffs do a lot more for melee than they do for casters. There are no castable spell damage buffs and intellect increases your spell crit by 1% for every 60 intellect.

If you're planning on running a caster team I wouldn't stress too much about maximizing every possible buff. For example, adding a druid into a caster group to provide MoTW and 3% crit aura might seem like a good idea but you'd actually lose DPS compared to just having another mage.

The only two really important buffs I can think of are windfury totem and blessing of salvation. Those two buffs actually do have a significant impact.