Personally I wouldn't even burn miles for domestic F to Hawaii from the eastern U.S., and especially not from the Bay Area. West coast to HA is such a short flight and domestic F isn't really anything to get excited about. Even if you won't fly international for a year or two, you might find it worthwhile to save a bit of miles for when it would be a better return on investment. Just my thoughts.
UA miles are useful for inter-island on HA, too, at 5K one way, if you're so inclined.