Clerical Weaponry Option

My group has long used the "Clerics use the weapon that their god uses" houserule, rather than the "guess I'm using a mace" rule.  I'm considering implementing a system in which this specific weapon gains increased bonuses and other powers as the Cleric advances; for example, a bonus of +1 when 3rd lvl is reached, +2 at 7th, +3 at 12th...  Special Effects will be included as well; the weapon of a devotee of a "Fire god" might become a flaming sword, or have the power equivalent to a Burning Hands spell twice/day, maybe even a Flamestrike option at higher lvl, while the trident of a sea god's Cleric could grant Water Breathing, Create/Purify Water, etc.  A special ritual must be performed by the head of the Cleric's order once the appropriate lvl is reached, or perhaps a quest must be performed... the specifics differing depending on the god being worshiped.  Only the Cleric can access these powers; for anyone else, the weapon is not magical.  Of course, the Cleric must be mindful to use these powers only in the service of the god, else the power will be revoked or suspended.  I like the idea of the Player knowing he's gonna get something cool - provided he earns it!  "Can't wait until I'm 12th lvl, and I can Disrupt Undead with my spear!"