As for the benefits: $/w already includes the electricity generated. California loses 1-2% of water in canals to evaporation; I think we can safely assume the economic value of preventing evaporation will be negligible when bare panels cost over $5/sq ft.
I look forward to seeing the author's economic analysis in the full report. However, the fact that these were the only numbers in this fluff piece suggests the economics won't be great.