My husband and I go to Europe from SAN almost every summer, and we have tried several of your possible scenarios. In 2015, we flew BA in business class, connecting in LHR, continuing on to Paris. We stayed a couple nights in Paris, then took the Eurostar to London. At the end of the trip, we did the exact same thing in reverse, staying in a different part of Paris. It was a lot of legwork, but a nice way to see both cities, and the price of two train tickets was still less than the difference in surcharges. Very nice trip, but a little tiring.

This past summer, we decided to go direct on BA for the outbound, splurging on F, and we returned in business class on AA. Keep in mind that the surcharges for London flights are higher for your return trip regardless of the carrier you choose. However, when you choose AA or DL you still save around $500 per person compared to BA. We felt it was worth the surcharge to try BA first class as a one-time novelty. The nose of the 747 was really cozy, quiet, and the service was outstanding. Seats were similar to what you get in Delta One for a lower price, but I have never had service on Delta even approaching the attentiveness of the first class flight attendants on BA.

As you continue searching for flights, you will probably find that availability in September/October is much better than during the peak summer months. Do search for round trip itineraries, and this will show Delta One, if available, at the 62.5K price point.

I think I would rather eat glass than fly from LAX. To me, it's almost always worth the extra money to fly from SAN and avoid that mess.