I’ve uploaded a paper—Raquel Alexander, Susan Scholz, and Stephen Mazza, “Measuring Rates of Return for Lobbying Expenditures”—which was published in 2009 in the Journal of Law and Politics. The key finding:
In this paper we use audited corporate tax disclosures relating to a tax holiday on repatriated earnings created by the American Jobs Creation Act of 2004 to examine the return on lobbying. We find firms lobbying for this provision have a return in excess of $220 for every $1 spent on lobbying, or 22,000%.
No wonder they do it!