[ericbsmith]

This is essentially no different than a race that can only see with Infravision or that can only hear and communicate with Ultrasonic Speech. Canonically, having an alternate sense is a 0 point feature if it's their only form of that kind of sense.

If they have Discriminatory Smell on top of being able to smell each other's pheromones then it's an advantage. If the only form of "special" smelling they have is to smell each others pheromones then it's not an advantage.

Under no circumstances is Mute appropriate if they can communicate normally amongst themselves, any more than it would be appropriate to give a race with Ultrasonic Speech Mute and Deaf.

Now, realistically communicating via pheromones would have some serious drawbacks, not the least of which is a slow communication rate and limited physical range (though the ability to layer speech over time could have some advantages). That would probably be worth points similar to having a speech impediment such as Stuttering. Of course, realistically no race could communicate complex thoughts via pheromones, it's just not an effective way of communicating at all.