As an OT for Cho-galls, intervene is invaluable.
Intervene the tank when Cho-gall firebuffs himself, throw up shield block and mitigate 2 hits and leave MT in easy mode for the rest of the buff.
Final phase healing is already a monster, rotating the intervene into the cool down rotation of the MT and healers provides such a high value.
Intervene is valuable but situational. Its value will go down as fights begin to be over geared and its benefit is just 'nice to have'.
I am finding I need to respec a ton lately, wish I had 4 specs: Tank single, tank aoe, utility (intervene, piercing howl etc) and DPS.