We live apx 40 miles from St Augustine and have been many times. St George street is the "strip" of the tourist district. St George street doesn't allow vehicles, but the side streets do, and they cross through St George street in at least one intersection. It can be a pleasant 30 minute one way stroll if not too crowded, but we have not been very impressed as we have gotten older.
The good: candy shops, leisure place to people watch IF not to crowded, a lot of resturants from all price ranges(finding them in all the nooks and turns is not always easy), easy walking access to the Fort(5 min's), easy access to the carriage rides if your into that. Nice Welcome Center with city info a small gift shop and bathrooms. the fort has large grounds for picnics, frisbee, etc.
The bad: homeless have been a problem forever, they need security more than ever, some stores and resturants are crummy, touristy more than historic, $10 parking at the information/welcome center(its nice, but it should be for $10), more bathrooms than ever, but not alot., shops not really open at night, if your a first timer it would take hours to walk all the side streets and get a good grasp of all the shops and resturants.
If your in St. Augustine you will be on St George street and it can be Ok at times. I wouldn't drive 10 hours to just visit the heart of this historic city.