New invasions happen and they eventually figure out the SCP and CCP systems. You'll end up with a few new power users with tons of SCP and CCP in a relatively short amount of time. These account can then be used for spam or other ulterior motives.
As a way to combat this, SCP and CCP could have a half-life wherein the faster you earn the points, the faster you lose the points. This half-life loss of points should be calculated relative to the rate of increase in points over time.
All users will constantly be earning and losing their points, so people who abandon their accounts will also lose their points and thus the ability to sell the high-point account. Those active keep lose or gain depending on their net activity. Consistent quality contributors should see a steady net gain. So the overnight successful invader will quickly lose the points as he will not be able to keep a consistent rate of increase.
Rates of decrease can be based on different factors like recent rate of increase, time on site, mod status, whatever other stats.
Let me know if this makes any sense.