Last year I stayed at the Doubletree in downtown and aside from the small, semi-pricey parking lot it was a great location and nice hotel at a decent price.
Petco Park is downtown and there are trolley stops there so for me that was a better location than Hotel Circle. Hotel Circle is great but I'd rather be a little closer to downtown, Petco, Balboa Park, the Zoo and Seaport Village than some of the other places. It's not very far from Old Town or the beaches either.
If you're looking for something fun I would kayak in La Jolla Cove. There are plenty of companies that do this but the one I went with was San Diego Bike & Kayak Tours. There's nothing like getting right up close to wild sea lions and kayaking into sea caves.
Sea World is always fun too of course. If you're going alone and have some extra cash look into the behind the scenes stuff (you can find it on the Sea World San Diego website), if you're taking a date spring for the "Dining With Shamu." The food is pretty basic but you can't beat an upclose encounter like that, just remember to keep your food dry!
In LA there are plenty of theme parks in Disneyland & California Adventure, Knotts Berry Farm, Universal Studios and such. I went to most of those a couple years ago and it was great but I REALLY enjoyed going to a taping of a TV show (Craig Ferguson). I wouldn't recommend waiting forever for the Price is Right unless you're a HUGE fan of the show and you have at least half a day to blow but it's an option. Check out 1iota.com for some free TV show tickets.
The one thing I'm probably going to do this summer is check out Medieval Times (located near Disneyland). I've never been and I'm such a huge nerd I feel it calling me hahaha.
If you want more specifics feel free to message me brother. I hope this helps!
My husband and I went to Medieval Times the 2nd year it was open and had a great time. It was very atmospheric and entertaining. At first it felt silly but soon even I was caught up in rooting for my knight! Of course that occurred in the LAST century! I hope you enjoy it.