If you are interested in hikes (1 - 3 hrs. as you mentioned) There are a couple in the back country about an hour drive from La Jolla on the way to Julian (Hwy.79). The first is Oakzanita Pk. Parking is easy on the side of Hwy. 79, and the hike is about five miles R.T. with almost a thousand ft. in altitude change. Take a lunch & a liter of water. Great 360 view of the local mountains. Another one up the road another 15 minutes is Stonewall Pk. (popular) at Paso Picacho State campground. It's about 1.5 miles each way & has another 360 view. The top is a rock peak with stone steps near the top and pipe railing at the top. You can park in the parking lot ($10). Julian is a fairly normal, small, mountain town you may or may not enjoy. The place we eat a lot there is the Julian Cafe. Another is Miner's Diner, which has an old fashioned soda fountain that serves many old time milk shakes, fizzes, sundays, etc. along with standard lunch fare. The town is full of curio, sweets, and apple pie shops. Many times the sidewalks are so crowded it's hard to walk and the traffic si sometimes backed up two to four miles coming from the north and south. So take that into consideration.
(I know if Paul looks at this, he'll want to kill me for not having any paragraphs.)

Yes. Do they still do the outdoor piano concert on Sunday mornings? I used to ride my bike there and round the velodrome.

If your adventuresome, consider crossing the border.
No bad days in Baja.
Puerto Nuevo -Lobster, rice, beans & fresh tortillas with a Margie overlooking the ocean for $20.00 per person.
4 star food & wine in Guadalupe Valley if you want a high end experience.
A lesson in humanity too when you cross back over.

Can't (generally) take a Rental across the boarder.

Oh and if you find a Porsche to drive, Lyons Valley Road....