NWP has always been a marginal economic proposition, even when lumber and gravel were big shippers. SP would make money from it for a few years, then have to spend a big chunk to reassemble the tinkertoys after a bad winter. Read your many NWP history books for details.

When the opportunity arose to dump the thing on the public, adding a little cash to the corporate coffers, SP took it. It was less complicated (legally and otherwise) and probably yielded a little more cash than scrapping would have been at the time. Remember, that's when SP was selling off a lot of the marginal (and not so marginal - see LA Metrolink) parts of its system, and pulling out second main track for scrap and relay wherever they could. The end game was obvious at that point, though for local freight service south of Willits it might have been managed better. Of course, the politics of the situation haven't helped the situation.

If it makes economic sense at all to run freight into the North Bay/Coast by rail it might be better in the long run to build 10 miles of new RR along Lakeville Hwy and abandon Marin completely. There's no practical and political possibility for rail service in Marin anyway, SMART included, and that gets rid of a couple of very problematic/expensive bridges (certain tugboat pilots would thank you). If you have to do a pile of EIS and other paperwork anyway to get running, as the judge says, you might as well get something useful for your trouble.