Spain

Personally, I generally consider one night as waste of time and effort. You lose a huge amount of time getting there, checking-in, then checking out, and back to the train station. I would be tempted to skip Arcos and Ronda or stay in Arcos two nights. If I skipped I would add a night to Granada. The Alhambra, itself, can take most of a day. Than add extra day to Sevilla with a stop over in Cordoba on the way to Sevilla. Or an overnight in Cordoba since it is between Sevilla and Madrid. This might an exception to my one night rule.

I'm concerned about all those one-nighters, too.

Toledo is very close to Madrid. I would spend all 4 nights in one city or the other if I didn't want to split 2/2.

I like Ronda and haven't yet been to Arcos. I'd hate to see you miss Ronda. The problem I see with just doing Arcos is that it leaves you a 6+ hour bus (or bus/train combo) ride from Granada, whereas you can get from Ronda to Granada in about 2-1/2 hours by train. I wonder whether it would work to see Arcos en route from Seville to Ronda and spend both nights in Ronda. That would require some sort of left-luggage facility in Arcos, and I do not know whether that is available.

I think it is fine. Toledo is a small city and easily seen with just one night (many people do it as a daytrip but then you miss the special character of the town at night when all the daytrippers and tour busses leave).

Arcos and Ronda are also small towns and a single night there is no issue and lets you get the feel for each at night. You could spend 2 nights in one and daytrip from there. Two nights in Granada is plenty to see the Alhambra and the other sites there. Two nights in Sevilla is tight but the main sites are the cathedral and Alcazar. Leave each for a day and fill in the rest of your time exploring.

What I was questioning was the hassle of switching hotels for just one night, but that doesn't seem to bother some folks.

I don't love one nights. If you've done them and are OK with it, then this is a good plan. Otherwise consolidate. I do like the idea of a night in Toledo, it's different after the day trippers have left. Arcos and Ronda are two one-nights back to back. Maybe pick one and day trip to the other. I can't recall the transit connections between the two, but it is something to look into.

Also, I personally think 2 nights is too short for Sevilla. I personally would skip Arcos and Ronda for more time in Sevilla (with a day trip to Cordoba), but this is a matter of preference. Ronda and Arcos are certainly worth seeing, I just prefer to dig in and skip short stops.

Finally, get your Alhambra tickets as soon as you have your dates nailed down - these go on sale well in advance and sell out fast. I already have mine for the end of May.

If you are visiting a smaller town or city, the time and effort to check into a hotel is pretty minimal. Daytrips, in fact, waste a lot of time commuting back and forth. The main factor is whether one is the type to unpack and spread everything out in their hotel room, or just live out of the suitcase. If the former, it does make it more of a hassle to stay only one night. And some people like to settle in and get a better feel while others are fine with no moss.

Day 1 Arrive Madrid - 3 nights
Day 2 Madrid sights
Day 3 Toledo day trip
Day 4 Train to Córdoba - 1 night
Day 5 Train to Granada - 2 nights
Day 6 Alhambra
Day 7 Bus to Ronda - 1 night
Day 8 Bus to Arcos - 1 night
Day 9 Bus to Sevilla - 2 nights
Day 10 Sevilla sights
Day 11 Fly from Sevilla direct to Paris