Once again, Cadfan said what Keterys and I have been saying. This doesn't seem to be clear enough, so perhaps this will help.
First, we have two cases:
- 1. A "property", as mentioned in the AV version of Enchant Magic Item, is only something like flaming (for a weapon) or deathcut (for an armor). If this is the case, the OP is incorrect, and this whole discussion is moot.
- 2. A magic item has a "property" if it has a line labelled Property: in its item description. If this is the case, the OP is correct, and the rest of this discussion ensues. For the sake of clarity, this means that you can use the ritual to add a property to an item which does not already have a property.
So, assuming case #2 is correct, we have a further two cases:
- 3. The resultant item exists already in some rules source. In this case, the ritual then follows the formula described in AV. That is, the ritual caster must be of a level equal to or greater than the level of the resultant item, but he only pays the difference between the cost of the initial item and the final item.
- 4. The resultant item does not exist in any rules source.
Expanding case #4 gives a final two cases:
- 5. Placing a property (as defined in case 2 above) in an item does not increase its level if the resulting item does not already exist.
- 6. If the resultant item does not exist already, it must be given an appropriate level. The ritual then follows the formula described in AV. That is, the ritual caster must be the same level or higher than the new item in order to cast the ritual, but he only pays the difference between the cost of the initial item and the final item.
I think we can all agree that following case #5 is patently ridiculous. As an example, this would mean that you can take your
+1 longsword and add the property from a Vorpal Weapon, with no cost or required caster level. So, the fact that there is no item which gives a +1 bonus on attack and damage rolls which also gives you exploding dice does
not mean that this item has the same level as a
+1 magic weapon.
Case #6 is what we are supporting. That is, according to the ritual as written, you can add the property from a Vorpal Weapon to a +1 magic weapon. But the resultant item has a higher level than a +1 magic weapon. This level might be lower than, equal to, or greater than the level of a vorpal weapon. The DM must determine the level of this new weapon, the ritual caster must be at least that level to cast the ritual, and the cost is whatever it would cost to make that item from scratch minus 360 gp (the cost of a +1 magic weapon). In other words, the ritual caster doesn't get any shortcuts - it ends up being
exactly the same as making the weapon from scratch, except that the item he is enchanting is already enchanted to begin with.
Depending on the base item and the property to be added, the end result's level might be in between the base item and the item which the property came from, or it might be of a higher level than both. It entirely depends upon the item and property in question; I do not believe that there exists a formula that can determine the proper level of such an item.
The onus is on the DM to give the new item an appropriate level. As long as this occurs, power creep is not possible. It is exactly the same as the DM having to assign an appropriate level to any custom item proposed by a player.
Hopefully that clears things up. I know it's long and wordy, but precision and disambiguity was what I was going for. I really think we're all agreeing, we're just not understanding each other fully.