Actually someone briefly mentioned it but it's a major tip... You can usually buy your SJC tickets such that the first and last legs are bus trips to SFO, and still get SJC pricing levels.

I know people very well (of course I'd never admit to doing it myself - but I know people VERY well) who frequently purchase these tickets, turn up and check in at SFO (because SJC won't check you in if your first leg is the bus to SFO) without ever getting on the bus, fly back to SFO and never catch the bus to SJC.

99% of the time these people also get the 250 bonus miles for taking the SJC bus service (but the bus trip is not a segment).

While you didn't ask it the reason for the price difference is SouthWest - SJC and OAK are cheap because of the SouthWest factor... the AA mini hub at SJC doesn't hurt pricing there either. Florida particularly has been on sale pretty much all year.