If you planning on staying in SF its self and you have a car you are very restricted without deep pockets. Lombard Street is pretty much your only option, you should be able to walk places from there but the hotels are motels and not the Wynn.
The other option is to ditch the car on the way in and rely on public transport around the city. You'll get a nicer hotel and be closer to the action but they are more expensive. We spent 2.5 days in SF and to be honest we didn't use the car other than coming in from the north over the golden gate bridge and popping down to golden gate park. We may have gone to Target as well for some snacks.
You'll have to get to the airport at the end but I don't think that will be a problem. I would go with the later as it is at the end of your trip and you don't need the car in the city. You can hire bikes for not a lot if you want to go up to the golden gate bridge. Dealing with luggage can be a pain though.
One thing to take note of when you do your trip, it is a good idea once you get your car to go to Target or Walmart and get some supplies like bottled water and snacks if you want them and leave them in the boot. The in town convenience stores are really expensive for drinks ($3-$4 a bottle), even for bottled water, in some places Gatorade was cheaper than water (NY). When its 30C outside you really start getting through it. But in Walmart you can get 30 X 500ml bottles of water for $4 or $6-7 for branded. Every hotel room has a fridge to cool what you need for the day. Things like fresh fruit is really expensive, well actually all fresh low calorie food is also seriously pricey compared to a UK supermarket. Burger and fries is cheap though!!
