The costs of patent litigation exceed their investment value in all industries except chemistry and pharmaceuticals. In the software industry, litigation costs are twice the investment value. Elimination of the patent system would increase the incentives for innovation in all industries except chemistry and pharmaceuticals by eliminating startup litigation costs.
Bessen, James (2008) The value of U.S. patents by owner and patent characteristics. Research Policy, Elsevier, vol. 37(5), pages 932-945, June.
Bessen, James & Meurer, Michael J. (2008) Patent Failure. Princeton University Press. <http://press.princeton.edu/chapters/s8634.pdf>
So it would make sense for patents to cover only chemicals and pharmaceuticals.