I've always enjoyed the festival events that come up. They add variety and sometimes a bit of extra challenge to the game. I espeically like collecting items over time to get that big payoff when I turn in certificates. Lately, however, I've grown frustrated with much of the garbage that comes from the festival packages. Here's my suggestion:
Festival event vendors. These vendors would trade a specific amount of festival certificates for specific items. For example, if there's a particular skin you're after, you could pay a certain amount of certificates for that item, rather than spending certificates for a CHANCE at some random item. More desireable items would cost more, while the current "less desireable" items would cost fewer certificates. Things like guild materials could still come in a random-chance package, and the random festival packages would also be sold at their current trade-in price.
I believe adding this feature would relieve a lot of the frustration long-time players have with the festival events. I also believe it would greatly enhance the festival experience for everybody.