Your route through San Francisco is OK but it is still basically urban streets and highways. Others have suggested some good alternatives to see interesting views and neighborhoods in the city (like Twin Peaks), and scenic rural areas south of the city (Hwy 9, 35 etc). But if you are musicians you should check out Santa Cruz. I don't play myself but there is a lot of folk/bluegrass in the area, and an active ukelele scene with a couple of good Hawaiian bars (Hula's, Pono) here https://www.facebook.com/UkuleleClubOfSantaCruz
And the roads from Sant Cruz to SF (not necessarily up the coast highway) are heaven.