Many of us avoid playing adventure mode as well as collecting goal rewards. As we level, the 72 Hour Card Flip event becomes increasingly impossible to the point it's barely worth attempting. No game should penalize players for playing new content. I honestly can't remember the last time I played the adventure map for this very reason.
If you're not going to fix that event's mechanic, could you at least give us an option of NOT collecting XP? Or NOT progressing to the next level? You have a system for collecting achievements, can't we do something similar (albeit more simplistic) for XP or leveling?
I'd really like to progress in the adventure islands again, but as long as you offer really good prizes for the 72 hour card flip, I can't afford to level any further. (As an aside, I love the idea of offering mediocre monsters for the 24 hour card flip. Higher players won't be bothered that it's impossible for them to complete, yet lower players can get themselves a "free" legendary. I thought that last one was awesome. Just perfect. Kudos.)