I've lived in Santa Barbara for 7 years and I've visited the Mission a few times. Once a year on Memorial day weekend dozens of chalk artists create amazing pieces of art on the asphalt in front of the mission. I highly recommend stopping by and watching them work if you have the opportunity.
Recently, during Fiesta weekend my mother (a 4th grade teacher well-versed on CA Missions) and I took the docent guided tour ($8 each for an adult pass) which lasted a little under an hour. The tour guide shared some interesting facts about the mission and the grounds; however for those with a background on CA history or it's missions I believe the self guided tour may be better ($6 each for adults). The grounds are beautiful and they have a well curated museum area you can walk through.
Parking is free and right near the Mission entrance. The docent tour is slow paced and the area seemed to be relatively handicap accessible. This is a great piece of CA history.