I am usually flying on my Aairpass, as that is almost always cheaper (and much more flexible) than buying a KUP or YUP. If you buy a good number of these fares, I suggest you look into it.

The MIA-SFO for $497 that you mention is insanely low. That would cost me about $1020 on my Aairpass. Whenever I've seen prices that much lower than the Aairpass price, the situation has always been that AA is having a sale, for whatever reason. Perhaps they are matching a competitor?

BTW, BOS-MIA is about $630 on an Aairpass, and the Aairpass completely insulates you from these price fluctuations. I simply cannot recommend it highly enough for people who regularly purchase first class.

The other nice thing about the Aairpass is that if A inventory runs out, and the only way to get into the first class cabin is to buy an F fare, it only costs about 20% more than an A fare with the Aairpass. If you are simply buying the tickets, full boat F typically costs at least that much more, and sometimes many times more than that.