Staying downtown, don't want to pay $24/day for parking, how difficult is it to get around without a car? ARe tourist spots (don't know what they are, either) accessible by mass transit, or do I bite the bullet? Any suggestions?

I think that San Diego is better with a car, but it can be done without one. Obviously there are places you wont be able to see easily, but there are also plenty of places you will.

SD has a lightrail system, which goes through downtown, so you will be able to pick that up easily. This line goes to Old Town and other places - I am sure you can find a map online.

There is a water taxi that goes from downtown to Coronado Island, so you can easily go there.

There is a hop on/hop off trolley that hits a lot of the major tourist sites. You buy a day pass and can ride as much as you want.

I am not familiar with the bus system at all, so I don't know how comprehensive it is, but again, I am sure you can find specific information on the web site.

This link should give you all the info you need:
http://www.sdcommute.com/

every summer we go to San Diego and spend a day getting around either by foot or mass transit. There is a lot to see downtown and the light rail goes to old town and other places. I'm sure ther are buses to Balboa Park which actually is not that too bad a walk from downtown (1-2 miles)

I go there plenty of times without a car. I use the trolley and bus and taxi. I enjoy walking too.

Sylvia,
How long and when are you going?

If a weekend and in the winter then you probably can get away without a car visiting Balboa Park, Gaslamp and Coronado.

If a for more than a few days or in the summer then I recommend a car. There are no beaches downtown. You have to drive/bus to them.

La Jolla, Del Mar, Mission Bay, Pacific Beach are better explored by car unless you are okay with several hours on a bus.