I read a pretty literal interpretation of the rules in the DMG, and the way I see it:
"...she gains the AC and unarmed damage of a 5th level monk. This AC bonus functions just like the monk's AC bonus."
The AC bonus a monk gets includes his/her Wis bonus, and a +1 every 5 levels. Also, since "This AC bonus functions just like the monk's AC bonus.", then:
"These bonuses to AC apply even against touch attacks or when the monk is flat-footed. She loses these bonuses when she is immobilized or helpless, when she wears any armor, when she carries a shield, or when she carries a medium or heavy load."
So, other than Clerics, Druids, and the occasional Paladin, not many non-monks are going to get much of an AC bonus due to Wisdom. Also, how many non-monks are going to be going around in NO armor, NO shield, and only a LIGHT load? Even if they managed to acquire a Monk's Belt?
Also, unarmed damage is the only thing gained by the wearer. So, that half of the belt's use is only useful in the obligatory tavern brawl, or for the 10th level fighter who actually spent one of his bonus feats on Improved Unarmed Combat.
So, basically, it's not very useful to non-monks. Most characters will end up with no AC bonus, and 1 or 2 extra points of unarmed damage, only after dodging an AoO.
DreadPollock