This would be the perfect way to test the duality series and hard-to-balance cards. It could be an area where you could make your own cards just for fun. (Wouldn't it be fun to make random cards that you know are too generic, but could also set up things like quest encounters or specific enemies in a mini-elements story?)
Even if the experts don't need it, the newbies might. Implement a UI for a "card customizer", give it to trainer- bam.