How about for the 2nd half of the granted ability: Once per day per cleric level, the cleric may take a full round action and use his Spot check instead of his normal attack roll to make one attack when using his deity's favored weapon. No bonuses to hit from a magic weapon, magic ammunition, feats, or any other source apply; unless the bonus adds to the cleric's Spot check. Penalties to to Spot checks due to distance do not apply to the Spot attack roll, this attack assumes the cleric already can see the target. If the attack hits, damage is delivered normally. Critical threat rolls revert to the cleric's normal attack bonus, with range penalties implemented.
In addition, Spot is a class skill.
So by comparison, let's take a 10th level cleric.
Normal ranged attack roll (BAB+7, Dex+3, Feats+2, Magic+5) = +17
Normal Spot check (Ranks+13, Wis+4, Feats+2, Magic+5) = +24