My suggestion is allowing 2 perks to be added to clan capes.
Before you explode with "OP", please consider the following.
As clan capes have 0 or low stats, it's not a direct or unqualified improvement over a skill cape with stats & a perk.
It's a sort of sideways step, but it may be useful for some skillers for example.
eg it's unlikely you'd use it as a combat cape with 2 perks, giving up the stats of your skill cape.
I thought this might again improve clan visibility, in a fun, useful but not overpowered way.
Of course the skill capes would need to be owned, & they would be consumed upon using with the clan cape.