I would like to suggest a possible set of simple Options for additional challenge and rewards at level 45-50.
All missions taken after level 45 would have an option of being played in one of three ways (toggleable through the Notoriety drop down):
1. Standard: No change to current challenge or rewards.
2. Alpha Only: Incarnate powers past the Alpha slot, and their Incarnate shifts, are Unavailable; completed missions give the mission owner a 60% chance for a single Reward Merit, level 45-50 team members get a 40% chance for a single Reward Merit.
3. No Incarnates: All Incarnate powers, and their level shifts, are Unavailable; completed missions give the mission owner a 100% chance for a single Reward Merit, level 45-50 team members get an 80% chance for a single Reward Merit.
These options would only apply to missions taken by level 45-50 characters that are of high enough level to allow the use of Incarnate powers, and only level 45-50 characters are eligible for the enhanced rewards.