As written I'd price it as 2500 gp cost not a +1 enhancement.

If we edit it so it has my changes then worth it (I bolded changes):
HEAVENLY BURST
Price: +1 bonus
Property: Weapon
Caster Level: 7th
Aura: Moderate; (DC 18) evocation
Activation: —
This weapon emits a low hum that sounds
distinctly like a chorus chanting slowly.
On a critical hit against an evil creature,
a heavenly burst weapon discharges a
shower of radiance that deals 3d6 points
of damage to the target and blinds it for 1
round. A successful DC 16 Will save
negates the blindness.
Projectile weapons bestow this prop*
erty upon their ammunition.
Prerequisites: Craft Magic Arms and
Armor, holy smite.
Cost to Create: Varies.