For which of these sights would you advise buying tickets in advance?

Since you are using the dorada cards there's no advantage to buying train tickets much in advance. The only ones that are likely to sell out are the Madrid/Toldeo tickets. You can buy them a day or two in advance to be on the safe side.

My hotel in Cordoba helped me buy train tickets and print them out. Or you can pick them up at a train station when you are there for a journey anyway. Best to avoid buying tickets in Madrid or Barcelona train stations, lines can be really long.

Thanks! That's helpful to know

Although I assume Chani's correct about the trains (that Madrid to and from Toledo is probably the riskiest), I have fairly often seen one or more trains along the Barcelona-Madrid-Cordoba-Seville route listed as sold out on the Renfe website when I was checking schedules for the next few days. I wouldn't wait unnecessarily until the day of travel, that's for sure. I also would get the Granada-Seville bus ticket a bit in advance. I have seen bus tickets sell out; it even happened to me once, in Bilbao. In my experience major inter-city buses in Spain tend to head out fairly full; I think they do a pretty good job of scheduling to meet demand. Even buying a day or two ahead of time, I am often assigned something like Seat 40, to give you an idea.

I do not travel to Europe at this time of year. My only vaguely comparable experience in Spain was April this year, but much of that trip was in and around Holy Week in Andalucía, which is a whole 'nother thing. With that caveat, I would want to have these tickets in my hand (or on my phone) when I walked up to the sight:

Casa Batllo
Casa Mila/La Pedrera
Seville Alcazar
Seville Cathedral (or buy combo ticket at Iglesia Colegial del Salvador)

I encountered a significant line at the Toledo cathedral, but that was on a religious-holiday weekend in 2016. Some folks here have reported no issues there, but just recently someone ran into a line (perhaps also on a holiday). At the least I'd check to be sure you won't be visiting the Cathedral on a holiday.

I have never seen a suggestion on this forum for pre-purchasing tickets to the Reina Sofia in Madrid (or the Thyssen). The Prado and the Royal Palace are maybe-yes/maybe-no. Weekdays may be less crowded at the Palace, which seemed to me to have a lot of Spanish visitors.

I do minimal pre-booking because 1) I have sleep issues and am not a morning person and 2) I allow myself a lot of time in each city, so I have flexibility about when I see each sight. For the more typical tourist, I would recommend buying advance tickets for high-traffic sites of particular interest, particularly taking advantage of the first time period of the day, when there's no risk of having to rush away from the previous sight to use the ticket. .

acraven - Thanks so much for your thorough and thoughtful reply.

Checking all sorts of forums, for this time period, for our trip in early November, we only pre-booked the Alhambra. Main reason is a lot of online purchase sites have a service fee. Also I am over 65, and many sites are either free or heavily discounted for over 65ers, but only available with proof of age at the ticket purchase site.

fincasaeharbor - thanks for your response. I hope that we can get the senior discounts at many of the sights. Some I've looked at do offer them online and Casa Batllo and La Pedrera are cheaper if booked online, but as our hotel is only a couple of blacks from those, I think I'll wait until we arrive to book those and I know more about whether there are any new protests in that area.

We're in Barcelona now and I bought tickets online for Cada Batllo and for La Pedrera as we were walking to them so that we wouldn't have to stand in line.