Adding buffs to melding will not break the economy. The game already does this on the other side of the equation by providing buffs to speed up spirit bonding. There should be food and Free Company actions available to buff melding success.
Alternatively, I would love a method that allows me to use more than 1 materia on a meld to increase the success of the meld. If a meld has a 10% chance of success, I would gladly use 10 materia for the meld if that meant 100% success just to remove the pain that comes with streaks of failures. This would have zero impact on materia demand and economy as the statistical average would remain the same.
