We will be staying two nights in the Gaslamp District before moving on to La Jolla and Carlsbad. Our plan is to rent a car when we head out of the city to La Jolla, assuming we can use public transportation around the city to Balboa Park, etc. Is that a correct assumption?

We stayed near Balboa Park and used the bus to get back from the Gaslamp District.

ediemay, you can use public transport, but it's slow and inefficient. It will probably take you some time and some transfers, generally, to get where you want to go. But if you're from out of town and aren't used to our freeways, maybe public transportation will be more relaxing...depends what sort of traffic you are used to where you live.

Enjoy your trip

Actually I was trying to be frugal I guess, Parking at our hotel is $32.00 a day and I figured if we were leaving it parked in the valet lot all day, why rent it until we head for La Jolla, but it sounds as though we will need it to go to Balboa , out to eat, etc.
By the way, how safe is it to walk around the Gaslamp district. I assume it is fine. One of the restaurants we want to go to is .6 mi. from the hotel . Walkable?

The area is safe and walkable. I think you'll be fine without a car, the trolly or bus will get you where you need to go, considering parking and traffic, maybe even more quickly than driving.

You won't need a car for the 2 nights in San Diego. The Gaslamp District has plenty of things to do that you can walk to. It's safe, lots of restaurants, Petco Park, Seaport Village, Horton Plaza, etc. You can walk to a bus, trolley, or ferry to take you most other places you'd want to go - Balboa Park, Coronado, Old Town, etc.

If you have a specific itinerary you want to do those two days post it and I'm sure we can tell you which mode of transport is best.

We spent a week in SD in February and only rented a car for two days (to go to the Wild Animal Park, Point Loma and to La Jolla). Otherwise from our hotel in the Gaslamp District, we walked all over the city and took the bus to Balboa Park and the Trolley to Old Town. I would definitely not rent a car until you head out of the city.