O'Farrell Street?
You've got kids and luggage. $10 or $20 extra a day to have your car nearby seems like the wrong place to save money. This is the kind of stuff your kids will make fun of when they are older. "Remember how Dad used to drive for an extra 30 minutes to find cheaper parking?"
My Dad's favorite restaurant in SF is Scoma's. Why? Free Parking. It's the 2nd best restaurant city in the US, and he goes to one restaurant.
I can be extremely parsimonious (ask my kids), but when we go on vacation, I do my best not to wince when my daughter orders a $20 breakfast and eats three bites, or when the speedboat rental costs more than the house -- because family trips are the things that everyone will remember forever -- and I want them to remember the fun things, not how Dad was trying to save a couple of bucks. You'll never miss the extra $10. Have fun!
Just one frugal man's opinion...