Petaluma see the wine country? Hmmm...didn't know that. Maybe small parts. Actually Napa is the start of the Napa Valley and is the main Wine Country. Though, there is the Sonoma Valley Wine Country and maybe you see that on your drive. The way I go to Petaluma, we don't see that, but I come from a different direction than you'll be going. Going to Mt. Tam is also beautiful & is north of the GGB.
I'm with you....you're not going to see Wine Country between SF and Petaluma...at least not without getting off the 101......
If seeing wine country is a secondary goal then Napas the way to go....but I still say if you want to go to napa hit the vacaville outlets....they're just 12 miles or so East on 80 from where you'd get off to go to Napa.
Or if you're like me....I'd hit vacaville....then napa, then explore my way north up the napa valley to the st helena outlets....
stopping for a picnic lunch at vsatui on the way....
damn I miss living in California!