If you like motorbikes you may like cars as well and I can recommend checking out ""Cruising Grant" Fridays in downtown Escondido.
My parents used to live there and the scenic route up to Mt.Palomar (Hw76 ) and down to Julian (Hw78 ) are brilliant, both on bike or in a convertible. Palomar is famous for its observatory, Julian for apple pie.
If want to check out the ocean, check out La Jolla Cove, Point Loma and the Coronado peninsula. I used to love taking the scenic routes from Escondido to the Ocean, such as Del Dios highway (along Lake Hodges) and Via de la Valle.
As for San Diego itself, on most lists you will find Balboa park, the Gaslamp district and Old Town.
If you like touring, you cannot go wrong doing the coastal route: old highway 101.
Up from Del Mar (check the racetrack as well) via Solano, Cardiff all the way to Carlsbad (Legoland
) and Oceanside (Marina).
You can't go further along the coast because of Camp Pendleton MCB. But if you take I:5 north, the area around San Juan Capistrano is very nice as well. Anything north of SJC is considered greater LA, but there are some great places there as well: from Newport Beach all the way to Long Beach.