17 Days in Spain + Portugal

Your itinerary is not too bad, but you skipped Madrid (and Toledo). Don't try to squeeze in Madrid, since you itinerary already involved much travel.

Ronda is good, but in my opinion the Costa Del Sol area of Spain is overrated.

You can see the Alhambra and more of Granada in one full day, which is pretty much what you plan.

Seville is the gem in you basket of places. I would spend more time there than in Barcelona.

Consider doing Portugal on a separate trip. Add Madrid with day trips to Toledo and Segovia. Portugal is wonderful, we love that country. We did a great week long river cruise on the Douro River. Amazing.
If you are staying in Porto, check out the wonderful B&B, The InPatio Guesthouse. Book early.

Skip Portugal and focus on Spain. Keep San Sebastian instead. You can always do a separate trip to Portugal. You could probably do Barcelona, San Sebastian, Seville, Granada, Cordoba, Madrid.

Great food in Seville and Madrid.

Of course if you already have your flights booked, then you are going to Portugal. Consider more days in Seville and reduce a day in Barcelona.

I don't think you have too much time anywhere. Assuming you're interested in the modernista architecture, you'll easily fill that time in Barcelona. And it has other sightseeing as well. I figure the arrival day doesn't really count because I, at least, am a zombie after a usually-sleepless overnight flight.

If you haven't already purchased Alhambra tickets, you need to take care of that very soon. General tickets are sold out (or site is closed) for the entire period December 24 - January 1. There are some more-expensive Dobla de Oro tickets, but they may evaporate soon.

Although Ronda is nice, I'd head straight to Seville. Your time there is going to be seriously short, and Ronda requires quite a detour (plus hours to see it), no matter whether you take public transportation or drive.

You were smart to leave the Basque Country for your next trip. There's a lot to see in northern Spain, and I imagine winter isn't the best time to be there. It's usually pleasantly cool even in mid-summer, and it rains a lot. It's a great destination when much of the rest of Spain is miserably hot, whereas San Sebastian gets about 7" of rain, on average, in December, spread across about 12 days. Not necessarily what you're looking for during the shortest days of the year.

There is great food everywhere. You can get pintxos in Barcelona. There's a small chain called Orio that have good wine selections, full meals and lots of pintxos (no tapas :-). If you drink alcohol, do order one glass of cider and have your camera ready when the waiter begins to pour it (better with video) There's one opposite the main entrance to the Santa Catarina Market. The best tapas in Spain are in Sevilla.

Overall I think your plan is very good. The only thing I don't know is what is open (sights, shops, restaurants) on the 24th-25th and 1st.