This is a good suggestion, but I think you mean to say in your OP:

Rank 50 character delevel-sync to rank 25 and enters rank 25 dungeon: loot and gear rewards are valuable to reflect the effort and difficulty required to complete the dungeon at the specified level.


Rank 50 character stays at rank 50 and enters rank 25 dungeon just for fun: loot and gear rewards are superficial and visual only - nothing that would be too valuable and ruin game balance because it took minimal effort for the rank 50 to blast through the dungeon.

Is that what you mean?