If I'm interpreting this correctly, does this mean you're changing event rates from a flat chance per sector to a flat chance per major world, and then lowering that chance overall to compensate? So that larger sectors like Sol sector would have higher overall event rate, yet the overall event rate across all Federation sectors averages to be about the same?
This does provide a convenient and logical way to slowly increase event rate: colonies advancing to major world status. The more major worlds there are, the more events there should be. (More major worlds should also increase budget, but by default they should increase member nation's own budget, with Starfleet having to explicitly ask for budget increases?)
This could also lead to the mechanism behind increasing event DCs: after certain thresholds of event rate, another event difficulty level as added at very low rate, and then event rates per difficulty increase in a Vancian way.
/musings