I very much like the idea of measuring what you're trying to do. Of course, extending myself to blogging seems have been a bridge just far enough, going to Facebook or Twitter is something I just haven't done. With no first hand experience, it follow that I'm in a poor position to give advice, not that that stops me.
I'm not sure what Twitter can do for USDA, but it seems to me the metric above suggests trying something different. If I were dictator for a day, maybe I'd offer a $5000 prize for the county employee who made the most innovative use of Twitter for FSA operations over the course of a year. Not sure how it would be measured, but I'm sure someone could figure it out.