The downside of the awesomeness of ambuscade capes is that several jobs can make good use of 3 or even 4 capes. I find this especially troublesome when it comes to making fast-cast capes. There isn't really a stat you can stack on a fast-cast cape to make it useful for a second purpose, and it's frequently only equipped for a fraction of a second. (My PLD swaps to an enmity cape, my casters swap to MAB capes, etc)
Tanks and melee would probably want a cape with Fast Cast / HP / Eva/M.Eva, Mages might choose likewise with MP or one with Fast Cast / MP / M.Acc/M.Dmg.
Putting HP or MP on these capes is only to sustain as much HP as you can while you cast spells. This is something I know well as my paladin loses nearly 1000 HP to WS
Likewise with oddball capes people might make for fun. WHM's undoubtedly love the Cursna+25 on their Ambuscade Cape, but for the melee WHM's, a blank melee-augmented cape would suit just as well and apply to any other mage they might melee on, or just any secondary job they want to try out but haven't yet made a cape for.
For the players that have already made a plethora of fast cast capes that might prefer to roll into one/two, you might offer a separate npc (so accidents don't happen) that will take any cape and give you half the invested materials back, so up to 10 thread and dust, 5 sap, 5 dye.