Had a similar dilemma today at SFO, but flying with UA to connect with NZ7 to AKL. The flight was brought forward by several hours, meaning I had to leave the house at 4.30am for a 0920 flight. I considered finding a left luggage place and getting on a BART but when all things considered, allowing a 2 hour period for getting through security at a more busy time, I would probably have had less than 2 hours in the city, so have spent it in teh very decent Polaris lounge eating a medium cooked burger with mushrooms and a fried egg, and drinking a lovely Calfornian red blend calle The Prisoner. Going into the city would have been an option but would have required more organisation than I have energy for...