Why not something cooler than darkvision?
- bonus to Cha checks because of their powerful presence and/or mesmerizing glowing dragon eyes
- take X less damage from attacks because of their hard scales (alternatively, +1 to AC)
- bonus to Con STs because of their hardy dragon blood
- a bite and/or claw attack
Cha checks and Con STs are not that good. The way racial AC boosts are, it only helps if you don't wear armour (otherwise, the armour will override your natural protection). They already have a breath attack that's bad because it doesn't scale well. A bite/claw attack will just be version 2.0 of that... aside from competing with said breath attack on how often you can use it, probably.
(I don't know about others, but dragon eyes don't portray much emotion or personality. I can only see it working with deception checks since they are inexpressive people).
