extra night in spain - where to spend it?

You're terribly short on time in Barcelona.

I agree with acraven, but it sounds like you may already have bought your plane tickets.

More than that, I think your itinerary has you backtracking. Toledo - Cordoba - Sevilla - Jerez - Ronda - Granada makes more sense. I would go from Toledo to Cordoba to Sevilla by train. Then pick up the car, drive to Jerez, Arcos, Ronda over 2-3 days and drop the car when you get to Granada.

Is this part of a larger trip to Europe, or are you flying in from far away and leaving right after? Exactly how to distribute your days would depend on that (for example, you start with "Madrid 2 nights"...if you're arriving on a redeye there, you only have one full day in Madrid, and a jet-lagged one at that). You'll get better advice if you 1) include specific dates, and 2) provide context of where you're coming from, and where you're going to, outside your time in Spain.

Agree with the above that you may consider adding the extra day to Madrid. We flew in from the U.S., arriving pretty tired in the late afternoon, and stayed 2N in Madrid. In hindsight, we would have liked to have added an extra night there.

However, we also only stayed 1N in Ronda, and I always suggest to people to stay 2N if you can, and have more time to explore other white towns nearby.

Also, not part of your question, but I will suggest anyway - you may consider not renting the car until you get to Cordoba. The fast train from Toledo (back through Madrid, I think) will be much quicker. Rent the car in Cordoba to continue your journey to Ronda etc.

Have fun!

Looking at how you've allocated your days, my inclination would be to drop a day from Granada and add both days to Barcelona. I also think that in a "perfect world", I would want two nights(if not more) in the pueblos blancos, but I don't consider Ronda very central to places like Zahara, Grazelema and Sentinel, and Arcos though Arcos is closer to Sevilla. I don't know anything about you, but for me, Madrid was a pretty low priority in comparison to the other great cities on your list. Madrid is fun and lively, but the other cities have so much more history and culture, in my opinion. I stayed two nights in Madrid, but spent one of the days in Segovia, which for me, was a great choice. However, if you are an art museum person, there is no question that Madrid has world class museums.

Is a lot this plan already booked? That is, you don't want to shuffle around the whole itinerary, but just add the extra night between Ronda and Sevilla?

If so I would add it to Sevilla. I'd have probably suggested that anyway since it's Spain best city, but in your case it would be convenient as well. You could spend the extra day in Sevilla, or take a second day-trip (e.g. to Cadiz).

An alternative would be to travel between Ronda and Sevilla via Cadiz and spend a night there, easy by car (otherwise lengthier journey of coach Ronda to Cadiz; then moderately quick train Cadiz to Sevilla).

Cadiz is very worthwhile stop, beautifully atmospheric (but no major individual sights), and is on the coast. Currently you don't get to the seaside at all in Andalucia, which seems a bit of an omission.

Separately, have you got your Alhambra tickets for Granada? If not, act now. And I'd drop the car on arrival at Sevilla (or Cadiz if you go that route).

Overall, I think your itinerary is fine and wouldn't suggest any major changes other than "inserting" the extra one.