Hello, my english is not good, but i will try my best :3
How about stacking the sticker. You would always get special stickers. Which with animation for example. Maybe something like this:
- glittering, (sparkle)
- red, green or blue luminous (like neon lights)
- moving
Or something else.
If you stack 5 common stickers you can get a rare Sticker. 50 rare Stickers > 1 epic sticker.
For this Idea you have to don't lose your sticker if start new after lvl 24. And maybe in a few updates you can also change the stickers with another members in your Clan.
Thx for your time, if you have some similar idea write it down