Perhaps tasks could be assigned karma award amounts by LW editors (Nesov, Eliezer, Louie, etc.), or even just one person who is appointed as the Karma Genie.

Some kind of democratic or market mechanism would more accurately reflect the value of tasks.

Also, there should probably be more incentives for gaining karma in general, as there are incentives for gaining upload ratio on what.cd. Rising through the karma ranks should give users special privileges that are actually desired.

The top contributors list on the sidebar could link to a page with the full rankings.