I think that the auto-stabilization property I described actually is desirable, though, so I changed the system to provide it. Now your super-bump power is: b*(1-0.15*^s/_b), where b is your base power and s is the total bump score you've contributed via superbumps over the last 30 days. This gives the same result as the previous algorithm except when any 30-day period overlaps with another.