If i cast Magic Vestment on my +5 Full Plate as a 16th level caster
Would i have a plus 13 or plus 17 to my armor class?
My buddie who is our Rules Guru said he saw it in Dragon that it works just checking
Transmutation
Level: Clr 3, Strength 3, War 3
Components: V, S, DF
Casting Time: 1 standard action
Range: Touch
Target: Armor or shield touched
Duration: 1 hour/level
Saving Throw: Will negates (harmless, object)
Spell Resistance: Yes (harmless, object)
You imbue a suit of armor or a shield with an enhancement bonus of +1 per four caster levels (maximum +5 at 20th level).
An outfit of regular clothing counts as armor that grants no AC bonus for the purpose of this spell.
Side Question why isnt this a paladin spell?
You will get +13 : 8 (full plate) +5 (magic enhancement).
The magic bonus of the armor and the spell bonus are both enhancement bonus, so they don't stack.
Because I've seen confusion elsewhere in posts, here's the full answer of why Magic Vestment bonuses don't stack with magic armor bonuses:
The "magical" part of magical armor is an "enhancement bonus", not an armor bonus, so it doesn't stack with Magic Vestment's enhancement bonus. Enhancement bonuses don't stack with each other, but there's a special exception for shields and armor:
Magic Armor bonuses are enhancement bonuses, never rise above +5, and stack with regular armor bonuses (and with shield and magic shield enhancement bonuses).
Shield enhancement bonuses stack with armor enhancement bonuses.
However, Magic Vestment also gives enhancement bonuses:
You imbue a suit of armor or a shield with an enhancement bonus of +1 per four caster levels (maximum +5 at 20th level).
You also cannot use Magic Vestment to give armor special abilities unless the spell specifies it specifically (which it doesn't), because you can't create a suit of armor with special abilities without also adding at least +1 enhancement, which doesn't stack with Magic Vestment.
A suit of armor with a special ability must also have at least a +1 enhancement bonus.
However, if the armor's enhancement bonus is less than the enhancement bonus provided by Magic Vestment, then you would take the greater of the two bonuses, meaning that if Magic Vestment gave +2 enhancement, and the armor's existing bonus was +1, then you get the better enhancement bonus of +2 (but they don't stack to +3), but the special abilities would still be available.