Who's a Good b... wait, I did that joke already.
The blink dog is a 4 RHD magical beast. It could've been worse (at least you get full BAB). The base stats are somewhat underwhelming: poor ability scores for a melee creature, a single weak natural attack and a shoddy skill list. Fortunately, the special abilities make more than up for it.
For one, blink dogs get 1/turn Dimension Door as a free action that doesn't prevent them from acting after teleporting. That's huge. That's literally the solution to the two biggest problems of each meleeer: how to reach flying enemies, and how to move and full attack in the same turn?
Secondly, they get a permanent Blink effect. Note, however, that it can be activated and resumed as a free action. This means you can begin your turn, drop the effect, attack without incurring a 20% miss chance, then reactivate the effect to gain the bonuses against incoming attacks. Not as huge as the teleportation, but still useful.
Taking those special abilities into account, I think the blink dog deserves at least +1 LA.