One of the Dylan websites is already showing 10 November as a possible second show in Chicago if the first sells out. Nothing about an extra LA show if the Hollywood Bowl sells out, though.
The Hollywood Bowl might well sell out, even with its 17,000 capacity, but would they fill it a second time? Maybe. Mabe not. You can bet there'll be a few movie stars and the like there. I imagine the after-show party will be something.
As dmg said, the Hollwood Bowl is an iconic venue, one that Dylan first played 49 years ago! It was in October 1963 and he was an unbilled guest at a Joan Baez concert, though his appearance was reported in the local pres beforehand. He played it in his own right two years later, one of his early "electric" shows, a show for which a recording circulates.
Now, why on earth did Dylan's website show a poster for a show with Mark Knopfler at the Hollywood Bowl on 25 August 2012? Goodness only knows.