I run the Hackers and Founders meetups, and we get a ton of people coming to the meetups that are visiting town for a week or two. The vibe that I get from most of them is that it's the trip is valuable.
If you are going to make a trip of it, I'd suggest coming in for a week or two. There's tons of startup/technology events and you can probably schedule one every night for the entire time you're in the area.
Bring business cards,introduce yourself to people at events, and you can be having coffee with people twice a day the entire time you're here. That's what being in Silicon Valley is about, and that's what's amazing about this place.
If you're not having a coffee with someone, spend the extra time in Palo Alto along University Ave, Mountain View along Castro Street or hanging out in bars and coffee shops in SF. I'd also suggest hitting Noise Bridge and the Hacker Dojo while you're here.