This is a continuation of the interesting chain of comments found here.
The incentive debate is interesting. Unfortunately, we do not have credible evidence about what value society should place on various aspects of the technology development process. We do, however, have hunches:
Invention: There are many of us who believe that the invention process is intrinsically beneficial wholly apart from disclosure of the resulting invention. Often, the result of invention includes new products or more efficient technologies that simply would not have been otherwise available apart from the innovation. At times, the invention may be used by the public without disclosing the invention itself. In those cases, the public still benefits because of the availability of the new technology. In addition to the benefit of new products, there is also an educative effect of innovative efforts. Even if a research initiative fails today, the researchers (and perhaps their organization) will have learned something that will help them in future endeavors.
Disclosure: Few (if any) inventions are stand-alone. Rather, inventors "stand on the shoulders" of those who have come before. Of course, the only way that today's inventors know yesterday's technology is through public disclosure. Now, disclosure usually comes from something other than the patent document -- such as released products, academic papers, etc. Disclosure also improves the potential for competition in the market.
For invention and disclosure, we also make the assumption that earlier is better.
One aspect of the debate on first-to-file is the question of whether more focus should be placed on invention or disclosure. Today's first-to-invent favors an early invention date, while the proposed first-to-invent system would push the (relative) focus toward disclosure.