[Suicide Junkie]

You could do that...

For each ship, if it is in orbit of a colony, boost experience up to a value that is some combination of the planet's population, conditions and the highest level of entertainment facility present.
If it isn't in orbit of a planet, reduce experience by 5% of its current value.

Adjust XP levels and descriptions as applicable.
Fleet XP would be the combat experience, while ship XP would be morale.