Yeah, that's the problem.
First, Silicon Valley isn't that profitable, relatively. A mere 5 counties that would all be (mostly) in the new "California" are responsible for a little over half our state's GDP ($2.7tn). Silicon Valley has a GDP of ~250bn.
But the real problem is that the new "Southern California" is screwed in this plan. They're left with arid desert, little industry, and a major population gap if my eyeball serves me. Nobody down there is going to vote for this. Nobody in California is going to vote for this. This is a NorCal Tea Party pipe dream.
Remember, this then has to go be approved by Congress.
It's so unrealistic it would be like jointly filing, as a Proposition on our November ballot, a "Yes" or "No" vote to send 69-69-69-69-69-69 with a massive state tax expenditure to the Super Lotto with our fingers crossed.