hmm. Yeah, this all depends on where you're staying.
For Port/LA, I think you'd be best served going to this:
The Lost Abbey » Port Brewing’s Annual Pre-Stone Anniversary Brunch
Green Flash is also up in that area, but I've never been to their brewery. Great beer, nice guys, but I'm not sure how user-friendly their brewery is.
Since you'll be in on the 20th, I'd suggest either Thursday or Friday (2-5 only - horrible hours...) going to Alesmith. Again, it is a small brewery, but they are world class, have most of their beer on tap when you go there, and you can buy bottles right from them. And Jess (the person who works at the tap room) is totally rad.
You could also hit up Ballast Point's Scripps location while you're in that area. You don't even have to get on the freeway to get there. If you go on a Thursday, there's typically a cask or a special beer on, so you might get lucky with that. If it is Friday, well, you still get good beer. They just remodeled and I haven't seen the new tasting room yet, but I hear it is bigger which can only be good because the place gets crowded.
The other Ballast Point brewery is also our LHBS, and is a bit further South, which is closer to where you get to the greatest beer hallway in So Cal.
If you start at Blind Lady Alehouse in Normal Heights, then move on to Toronado, and then Hamilton's Tavern, and if you're feeling adventurous, all the way to downtown Johnny Brown's. There's a bus that goes between all but the Blind Lady. There are more beer bars on 30th as well. Ritual Tavern is a small restaurant with good beer. There's a place called the Linkery that I won't set foot in because the owner is a dick. There are a few others as well, but the 3 I mentioned (plus DTJBs) are your best bet.
Blind Lady Alehouse is owned by Lee Chase, of Stone brewing fame. They make pizza and salad and stuff like that. Toronado is loud and sterile, but has great beer, and Hamilton's is sort of the perfect bar. Great beer, shuffleboard, a better jukebox now that they switched it out, and the best atmosphere in SD.
As for brewing, I'm pretty sure I'd be down for a session on the 23rd if you wanted to do so. I could fire up my system or we could do it at someone else's house. My house isn't conducive to multiple brewers, but my old system is portable enough that I could throw it in my truck if we wanted to do so.
OH ****! I forgot Pizza Port. Pizza Port in Carlsbad is a must see. It is North County SD, and along the same corridor as GF, LA, Stone, etc., but is close to the coast, walking distance to the train and the beach, and has an amazing bottle shop next door. Food is good, lots of guest taps, and Jeff Bagby is a great head brewer.