Originally Posted by
Elyoric
Haven't ran a low level dungeon in quite some time, are they still pull everything aoe-fests? Even so, unless your tank was outfitted in cloth or trying to pull half the instance, you should be able to heal without issue as shadow spec. Additionally, you should be able to heal as that spec into your 50's.
Hell, you shouldn't even need a "real" tank for those instances. Any 4 random dps can work; they can be shaman tanked or even hunter pet tanked. Personally I've tanked them as a arms warrior, healed as a shadow priest, and solo'ed much of SM as a hunter all at the appropriate dungeon level, so I'd be curious to know what was going on in your dungeon run.
A minor point, but shield and flash heal are your most mana-inefficient spells so they should be emergency only.