In all honesty, I always got the impression that the point of twitter was to tune into other people's noise, not to harvest useful information.
I think a quick and neat workaround would be to assign "importance" levels to folks you follow. For e.g. @billgates might be a '1' whereas @amanda9875 might be a '5' - so while you get every tweet @billgates sends out, you might only get every fifth message @amanda9875 tweets.