Travel from Sevilla back to Barcelona?

To me it would depend on cost of airfare. Since the tour ends in Sevilla, I'd fly home from there or Madrid. Looking at that itinerary, if it were me, I'd do 1-2 more days in Sevilla, take a train to Cordoba and spend 2 days there and then head to Madrid. Cordoba is a wonderful city and its conveniently between Sevilla and Madrid on the train line. In addition to the wonderful Mezquita, Cordoba has a pretty riverfront area, lovely gardens of the Alcazar and the amazingly beautiful Jewish quarter and its patios.

Seville to Barcelona is a fairly long train ride, 5.5 hours. That means travelling the day before the outward flight. Only worth it if the airfare is much lower than a multi-city US-Barcelona / Seville-US or, alternatively US-Barcelona / Madrid-US. So, check airfares on your dates.

Madrid is quicker than Barcelona to get to from Sevilla (or Cordoba) if there are direct flights from there going to your home airport. But given you have to travel anyway, you could consider flying from Sevilla airport and making a change at a European hub from where there are lots of transatlantic options - there are flights (some seasonal) to major airports like CDG, Gatwick, Amsterdam, etc. Or from Malaga airport there are more choices (and more frequent services). I've been there queuing behind Americans checking-in for the BA/Iberia flight to Heathrow then onwards to the US west-coast.

I guess you need to play with the timings, connections and costs to see what suits best.

What tour are you on? Without knowing what you've already covered, I'd suggest you want at least three nights in Sevilla, ideally four, and more if you plan day-trips. If Cordoba isn't already on your itinerary, I'd agree with the previous poster that you should add that - at least as a day-trip from Sevilla (or stop on the way to Madrid), but preferably as a proper visit for 1 or 2 nights if you have the time.

Check airline prices from Seville vs Madrid vs Barcelona to your home. Usually Madrid is the cheapest but it may be that you can travel from Seville back home just as cheaply. Not sure what Spain tour you are taking but most RS tours cover Seville pretty throughly. I'd actually spend another day in Barcelona before the tour.

If Madrid isn't part of your RS tour than I'd advise at least a day or two there before leaving. Mostly because Barcelona is a very international city whereas Madrid feels very Spanish.

Flying open-jaw Barcelona-Madrid (choose multi-destination option when searching flights).

Which tour - Best of in 14 days or My Way in 11? Either way, you'll spend time in Madrid so you probably don't need more days there. Just take an afternoon or evening train and spend your last night there so you can get to the airport easily. If you stay at the Europa (one of the RS tour hotels), there's convenient public transportation just meters away.

There is so much so see in and around Sevilla, you could easily fill another week. Jerez and Cadiz are easy day trips from Sevilla by train, and there's a lot to see in Sevilla that the 14-day tour doesn't cover. Cordoba is my favorite Spanish city and a good place to stay for 1-2 nights and take it a little slower after the tour. Please don't skip the Mezquita and Juderia there, as an overnight stay, a day trip from Sevilla, or a stop on the way from Sevilla to Madrid (there's luggage storage at the bus station across the street from the train station in Cordoba).

I am delighted by the responses to my simple request.

Background: we will depart from either SFO or OAK in California. The trip is Best of Spain in 14 days from August 26 thru September 8.
All of the suggestions are interesting! There are so many great ones!! A side trip to Cordoba was mentioned by several!!
I will check all in detail.
Next question - insurance. Has anyone purchased a medical evac supplement? Unfortunately, I have had 2 friends who were hit with sizable bills.