I'm on the bus in SFO and flying is looking a lot more like RJ flying. That's the 'disadvantage' of mainline picking up a greater amount of RJ flying. If that's the price to pay to get the flying back to mainline, I'm OK with that.

As for Santa Cruz/any surfing hotspot in the Bay area, there are a decent of pilots who live within a couple of hours of SFO. When I was 777LAX (it was a very small base with few flights), a lot of local senior FOs would bid reserve and surf all day. YMMV on the guppy since it's a much larger base.

As long as hiring and vacancy bids continue at the current pace, you will be on a quick upward climb for seniority in SFO. However, you will hit a point where you start noticing that most of the pilots below you are bidding out of SFO - this should start after you've already got a line. At that point, you'll move three steps forward (newhires) and two steps back (vacancy bids). Those leaving will be going to DEN, ORD, IAH, LAX, even IAD.
But as others have mentioned, SFO and EWR are the junior bases so your seniority will always go further in those two bases.