Paulie, I meant state dues-payers.
For salary as overhead, you could try to pro-rate it by how much staff time is spent doing politics that wouldn't otherwise have gotten done. I can't recall our last ED (Angela Keaton) reporting any such activities at the ExCom meetings I attended. She only talked about renewals and fundraising and database maintenance etc., all of which I'd classify as overhead.
Vote totals of winning candidates is certainly the metric that the current LPCA administration would emphasize, as they are firm advocates of a bottom-up farm-team strategy. Looking at the 6 elected municipal officials listed at http://www.lp.org/states/Texas, one of them is in a town of 4000, and the rest are in towns of under 2000. LPCA has an elected county supervisor (Tom Tryon) who alone has as many constituents as all 6 of these Texans combined. John Inks, who was just elected at-large to the city council of Mountain View (pop. 70000), has several times more constituents than these 6 Texans. If you start looking at school boards and special districts, the disparity grows even more. Even my modest water board seat has twice as many constituents as are in that Texas town of 4000.