While doing my roulettes I'd often get triple triad cards that I have already obtained. These fill up the inventory, and in order to trade them for MGP I have to actually go to the Gold Saucer to do so.
The cards are worth very little, so teleporting to the GC to claim the MGP does not feel worth it. If the idea is to bring us into the GC, I don't think it's a valid reason since people are just there for a few seconds to trade the cards then leave. There are other minigames who's purpose better fulfill the "go to GC" criteria, like the daily mini cactpot.
Teleporting to the GC just to clear my inventory breaks up the flow of the game and what I'm doing.
I suggest just allowing us to use the card for MGP directly from inventory, or allow us to sell the cards to retainers for MGP from the summoning bell.