My wife and I will spend six nights in San Diego: three nights at the Heritage Park B&B in Old Town and three nights at the Hotel del Coronado. We plan on staying close to town - shopping at Horton's, a concert at Humphrey's, bar hopping in the Gaslamp district and beaching it in Coronado.
Question: do we need to rent a car?

You can take the trolley from Old Town to Horton/Downtown (Gaslamp) easily,roundtrip. The Coronado leg of your trip you will be all set walking around. But to get to Humphrey's/Shelter Island (8 miles?) you will need to take a cab or rent a car because there is no convenient public transpo (bus). Oh, how do you plan on going from Old Town to Coronado (about 15 miles)?

We will get a cab the morning we check out of the Heritage Park Inn. I think the expensive cab ride will be more than offset by the money we save by not parking a rental at the hotel Del. Thanks for the reply.

not even close to 15 miles to coronado from old town. drove a cab in sd for 10 years. $20 cab fare, tops.

Yeah, I hear you. We will be paying $15 a day to park our rental at the Coronado Marriott! If we didn't need our car to get to SD from LA airport, we'd go carless too.

Maggi,

If airport transportation is your only need for a car, consider one way car rentals. We often do that when flying out of LAX.

Check all agencies each way because sometimes LAX->SAN can be cheaper for one company and more expensive for SAN->LAX

Maggi,

Just spent four nights at the Coronado Marriott and parked on the street the entire time. Lots of parking available on the street, less than a block from the hotel. Check it out before you pay the $$$.