Well yes indeed I also believe that CL attribute is a better (and standardized) way to interpret a wand's power, but there's a very important advantage of the +X descriptor: it is quick and easy to tell which item is better. When you move the cursor over the item, it will be in the name of the item, therefore you can make minute decisions e.g. which to sell, which to buy, which to drop etc... The CL would look out of place in the name field, which means that the only way to differentiate would be the open the item description and this takes time.
Tbs, I was once working on a standardization to provide a CL to all items with enchantment level, mostly to all weapons, armors and shields so that there would be a general rule for all their possible traits:
- on hit effects
- equipped effects
- charged abilities
- per day abilities