That item already exists, it's the
Amulet of Mighty Fists.
The better question is, this item obviously does not fit the protection and discernment affinities of the slot it's in, so could you get it without that 50% markup in a different slot?
Let's see, I suppose transformation might fit for cloaks but it's a little bit of a stretch and I think you already have a cloak; a shirt's physical improvement might fit since these are
natural weapons being enhanced; combat for bracers is obvious but you already have Bracers of Armor; the destructive power affinity of gauntlets fits but that would conflict with your Gloves of Dex; belts have physical improvement just like shirts so that might work, but I don't know if you already have a magic belt. It looks like getting it on a shirt is your best bet, pending DM approval.
BTW, does a robe's affinity for "Multiple effects" mean it costs less to add extra abilities to a robe than for other slots?
Also, what kinds of abilities go well on robes? "Multiple effects" is the only thing listed.
