In my little corner of the world (the West San Fernando Valley), I found one restaurant offering 20 miles per dollar:
Cavaliere Ristorante
Italian (Red Lion Inn)
CA, Los Angeles
San Fernando Valley West of 405
20200 Sherman Way
Canoga Park, CA 91306
(818) 676-0885
There are also quite a few restaurants now that allow unlimited visits. On the downside, there are now many restaurants only offering 5 miles per dollar, which is not much of an incentive.