In LA the 2 hotels in the Pico/Robertson area that are closest to the kosher food options are the Residence Inn and Crowne Plaza. There is also the new Mr. C Beverly Hills Hotel (formerly The Tower). These places will allow you to walk the Pico strip of restaurants and shuls.
In terms of things to do LA has plenty: Rodeo Dr., Disneyland, Universal Studios, Venice, Santa Monica, Malibu, Hollywood... plenty to keep you occupied I think for a few days.
Vegas mid-week you should be able to find places like the Venetian/Palazzo for about $120 a night... if not cheaper on Priceline.