Honestly, i have been thinking about that point.

I think that some kind of tournament should be interesting. Then you can use boosters, with some purpose, or develop your character to win the tournament, given that the first one, the champion, will be the strongest.

The reward could be similar to the contest, or perhaps more, depending on the number of participants. I know that this is difficult and needs time. But there are games that divide the characters into different leagues according to their level.