Tadich grill is good for historical significance but it's nothing special in terms of food. Not far from where I used to live. The Embarcadero is kind of cool and you can take the boat to Alcatrez. If you have your car you drive across the GG and drive through Marin Headlands. I think that's pretty cool -- great views of the city and cool to see the bunkers looking for a Japanese attack in WW2.
Lot's of cool neighborhoods to walk around: Russian Hill, the Marina, Nob Hill, Chinatown, North Beach, teh Warf (a little touristy) ... I think it be cool for your dad to see the various neighborhoods which make SF unique.
Hope you guys have a lot fun.