As Bruno Pereira says, "No one cares about karma in launchpad (at least not to be worrying about it)," and I consider that a feature, not a bug. Asking and answering questions is important, but there's little risk that people will think AU rep is a measure of someone's overall contribution to Ubuntu, because it's readily apparent that many other things that go into Ubuntu --like like writing actual code and debugging it until it seems to work right --happen happen mostly in other places. In contrast, Launchpad is the broader of the two sites: it has answers, but also bugs, code, blueprints, and translations, and covers way more projects than just Ubuntu.
In conclusion, I don't think it would be good to incentivize scurrying to maintain a high rate of posting. Reputation is a compelling idea -- more compelling, perhaps, than it should be. If any major change to the reputation system on Ask Ubuntu (and, more generally, Stack Exchange) is to be made, I think the goal should not be to increase the power rep has over us. If anything, it would be best to decrease the amount of motivation that comes from rep, so as to encourage us all to work on the things that which interestsinterest and inspiresinspire us.