Maybe it depends on what you mean by "recipe for success of Silicon Valley" but I doubt weather has primary influence on the recipe. Sweden, South Korea, and Switzerland are considered the top 3 "innovative economies"[1] in the world and aren't particularly notable for their weather.

[1] usually this means a mix of #patents filed, number of phds/100,000 and r&d expenditure/gdp. Not sure how you would rather measure the success of silicon valley to set it apart.