As to your valuations, yes that is one way of doing it. I think it's interesting though that if you subtract CY's stake in SPWR from CY's market cap, you are left with a measley $130 million based on today's closing prices.
If CY stays at this level and SPWR pops $2.5 (yes exactly 2.5), the market value of 52+ million SPWR shares will slightly exceed CY's market cap.