XP bonus is 45% on gen 16, it's pretty damn important if you're going for level 34 or higher.
But I see that you're talking about Strategus. I guess that being level 31 matters in Strat, but I never really played it so I don't know for sure.
Edit: There's simple solution for this. Make it one time deal or make an event that happens every 6 months that allows high level folks to retire.