There are really sooo many things to do besides DL....
.... just hopping into a car you could explore for weeks! But that would be pretty inefficient. So - if you don't mind I'll drop a few general suggestions:
1) tickets for anything (sports or performing arts). Searching ebay and selecting any tickets in any number for the greater LA area in september comes back with 1,921 auction listings (lots of sports). There's gotta be a few dozen if not a few hundred listings good during your 10 day stay. I assume your 2 free days are flexible... and if you're wise then you would agree that the best days to skip the park are on the weekends. Which is great for catching live entertainment.
2) explore one of the many museums in the area. The Getty is the richest museum in the world near Santa Monica. There is a Peterson Automotive museum. Or visit the Aquarium of the Pacific in Long Beach. Etc.
3) Ride bikes along the beach. Catch lunch right along side the sand and watch folks ride by. Low key, very pleasant.
4) Visit another amusement park - like Knotts Berry Farm, Universal Studios, or maybe Magic Mountain which is furthest but an all rollercoaster place for the most part - plus a water park if it is still open and the weather is fair.
5) How about doing some shopping - unless you get good shopping back home?
6) Tuesday sept 26 Tom Petty and the Heart Breakers play at the Hollywood Bowl. On Sept 30th at the Greek Theater is WaveFest: Earth, Wind and Fire, Ramsey Lewis Trio, David Pack (29.50-129.50). On the 29th WaveFest features : Brian McKnight, Boney James, Eric Darius, Norman Brown - check out the regional line up at
http://www.casenet.com/concert/concert.html
7) more later edited in