Well, if you only have a couple hours to go out of your way, then taking PCH may not be an option.
So, if you take I-5, then I recommend you stop at Harris Ranch for a meal. Assuming you like Steak, that is. Harris Ranch is in Coalinga, is about half way. Driving Directions. The steaks are awsome.
In Los Angeles, there are TONS of things to do, many of them inexpensive.
On your route, there is Griffith Park, if you want to get out and take a walk.
If you take I-405 thru Los Angeles, then I highly recommend taking in the J. Paul Getty Museum if you like culture. It’s right on the way, and FREE (well, parking isn’t, but admission is.) If you do one thing on my list, this is the thing to do.
If you’d rather visit a winery, then I recommend the San Antonio Winery just east of downtown. It’s a bit of a detour if you’re just passing thru town, but the food is excellent, and they have a large tasting room.
In San Diego, I recommend the San Diego Zoo above all else. Sure, you can go to La Jolla or Sea World, or the Gas Light District, but you’ll drop loads of cash there for stuff you can see in many other cities, but their Zoo is by far their most unique attraction. Plus, you can go at night when it’s cooler. Not that San Diego is all that hot in the summer.
There… that’s enough for a couple of days of distraction, at least… and it’s just a tiny sample.