Not trying to convince the OP to stay, since it sounds like a decision has already been reached based on sound reasoning.
Given the fact that AA does not have any nonstop/non-codeshare international departures from the Bay Area, it might be easy to dismiss it as a viable option, but I too have found flying AA out of the Bay Area to be extremely manageable:
1. Good coverage to Asia/Australia on AA partners (Cathay, JAL, & Qantas)
2. Doing a connection in ORD, JFK, or even DFW for flights to Western Europe yields decent coverage to the major cities. And I prefer to connect in the good ol' USA instead of Europe (and LHR in particular).
3. Alaska/Horizon do a great job for flying up and down the west coast.
4. AA security line waits at SFO are almost non-existent
5. I feel that there seems to be lower percentage of elites on AA than UA making upgrades easier. This is not hard fact - just a soft conclusion based on an anecdotal evidence arising from conversations with colleagues.
6. AA routinely beats out UA on pricing for my itineraries which makes the bean counters happy.
7. And of course an AC with a great staff. Size doesn't matter. Or so I've been told.
The major gaps I've found have been SFO-DEN (mentioned by the OP), SFO-PHX, and SFO-SLC. If I needed to fly any one of those routes on a regular basis, I would seriously consider switching. I would be crazy (FT MR translation: quite sane) to want to connect on those journeys.
To the OP - good luck, but you wouldn't be alone if you decided to come back to AA
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