Conversion Benefits

A recent thread raised the subject of clerics converting unbelievers to the faith. Unless the character's religion is modeled on a real-world religion that practices conversion, it's not something I see as intrinsic to a cleric's faith; however, if a player chooses to play their character as a missionary, I figure the benefit of making a convert should be a temporary bonus on Turn Undead rolls, or the "clerics without spells" equivalent. Perhaps a bonus 1st level spell for one day under OD&D/CD&D/AD&D standard rules, or a 2nd level spell if the convert is a higher level than the cleric.