Hi, S....
I have spent 3 summers in San Diego when I was on staff with CCC working with students. Sea World has a lot of things to keep you busy (most of our students worked there). They do have lockers and stuff, and you can exit the park and get back in if you need some down time. I'm not sure about hotels, as we were there for the long summer and were in Mission Beach. My hubby and I have had good luck pricelining hotels, so you might try that or see if you can get a deal through a travel agent on a package. The beach is nice. Mission and Pacific beaches have your typical boardwalk feel. Belmont Park is down on Mission Beach--it has a wood roller coaster and some other rides. Pacific Beach also has a boardwalk at it's end. Mission Bay is nice, too. It's across Mission Blvd from the beach, but is a bit quieter with a walking trail around it. If you go down to La Jolla, there are seals that hang out on the big rocks and there is a park/beachy area. I haven't done the whale watching, though have heard it's fun. Disneyland and California Adventure are fun...California is not so crowded and you can get a park hopper if you want to go back and forth. TJ (Tijuana) is a unique experience--you just may want to check into the passport thing with the changing policies...not sure when that goes into effect. You might want sunscreen, bottled water, and toilet paper/kleenex if you go over. Shopping is good. One thing you can do in the city is spend a day doing a trolley tour. The trolley tours start in Old Town, and you can basically ride the loop for the day--you just have to make sure you catch that last trolley back to old town at the end of the day. You can get off at any or all of the stops, and it takes you to all of the highlights of San Diego. Some of the stops include downtown (Gaslamp Quarter), the Harbor (which has the Midway Aircraft Carrier and The Star of India ship you can pay to tour--you can also pick up whale watching there, too), Balboa Park (all kinds of great gardens and museums), the San Diego Zoo, and Coronado (make sure you go get ice cream up at the Hotel!). It can be a nice option because you can pick and choose whereever you like and move on whenever you want. The website for Old Town Trolleys is http://www.trolleytours.com/San-Diego/ You also get a San Diego Day Planner booklet with the ticket. Old Town has great Mexican food. They offer a 1 or 2 day trolley pass, which if you know you want to see and get around a lot without having to take a rental car, it might be worth it. Also, if you like nature, Torrey Pines nature reserve is north of the city and is beautiful. There are probably a lot of other things, so feel free to email me if you have more questions. Sorry about the long reply, but I do love San Diego!
:) Have a great trip--
V.