There seems to be new outfits coming out all the time now, with one outfit costing 700 gems. Those are free to apply and change any time.
The gemstore armors are not any cheaper, some costing 800 gems, however they cost 1 transmutation charge to apply.
Since people already bought them with gems, I suggest that for items that you buy with gems, they should cost 0 transmutation charge to apply in the wardrobe. (similar to items like Radiant/hellfire armors)
I think more people will vary their equipment looks on a more frequent basis.