Mapache
Explorer
Right. This is the (intended) drawback of auto-hit powers like this, they get very few damage boosts.
Magic Missile is "auto-hit" (which really means it's auto-damage and doesn't hit at all), but the reason it's low damage is because it has no damage roll, which is entirely separate (see powers like Prismatic Strands, which roll to hit but have no damage roll). Most damage boosters apply only to damage rolls, not to damage in general.