Barcelona, Madrid, Segovia, Toledo, and Seville itinerary ideas??

Why not just go to Segovia and Toledo? We don't all have to find the same things interesting. I like small places; I don't worry about it. But you know Barcelona is a big city too, right?
Instead of doing the bus tour in Madrid, I would pick one of the more atmospheric neighborhoods and just focus on that instead.
One of our regulars here has been talking up Zaragoza and it has really moved up on my list of places to visit. You might read up on it and see if you'd like to stop there en route to Madrid.
Highly recommend Cordoba too.
How much time do you have, and are you flying from Sevilla to Porto?

Need to know the total number of nights you have available after spending 4 in Barcelona.
Easy answer on Madrid..........
1) Madrid is renown for its museums and is viewed as the capital for museum experiences. Do your research on the variety of museums offered in Madrid.
2) While Madrid its the third largest city in Europe it offers a condensed historical area offering a variety of opportunities to experience. I recommend two nights in Madrid. BTW: the train station is incredible.
3) Spending a night in Toledo is an excellent experience.

Ok, saw the answer of 8 nights for Spain prior to Porto............
Our travel style is about "being there" instead of "seeing there" and while you can do it, I think you are shorting the opportunity to create wonderful memories of travel. Step back and consider the distances you are proposing to cover.
Barcelona - three nights, although well worth four
Madrid - two nights with a day trip to Toledo
Seville - three nights

DO NOT do a double bus tour of Madrid. Pull up a map of the old town area and recognize it is easy to walk and more engaging by doing so.

I truly believe the rewarding journey would be four nights in Barcelona, fly to Seville and spend four nights with a day trip to Cordoba.

Firstly, I agree with steven’s suggestion for a more rewarding journey.

Because you don’t want to visit museums in Madrid, which I think is Madrid’s big draw, I would omit Madrid and visit Barcelona for 4 nights and Seville for 4 nights. You only have 8 nights, right? Or drop a night from Barcelona and drop a night from Seville and spend 2 nights in Granada so you can visit the Alhambra which is outstanding. Still a rushed trip but that’s all the time you have. I have been to Toledo but not to Segovia. I would choose Granada and the Alhambra any day over Toledo.

Have you already purchased your airline tickets? If not, I would omit Barcelona, the outlier, and concentrate on Andalusia. You could spend 4 nights in Seville, and 2 nights each in cordoba and Granada. These are smaller cities with very important and beautiful cultural and historical sites. And each city is very different from each other visually and architecturally with its own special ambiance. Granada has the amazing Alhambra; cordoba has the magnificent Mezquita; and Seville has the stunning Real Alcazar among other beautiful sites!

Both Sevilla and Barcelona are big cities too. Not knowing what you like to do, there’s no way of knowing what specifically to recommend. Popular places in Madrid include the Plaza Mayor, Royal Palace, Temple of Debod, Puerta Del Sol (if construction gets finished) and Retiro Park. There are a number of markets, but none that can match the Boquería in Barcelona. Lesser sights might include, Cibeles fountain, Neptuno fountain, Toledo bridge and gate, Alcalá gate, and Plaza de España. If you like the art of Francisco de Goya you could visit the small Ermita de San Antonio de la Florida. It’s his burial place and has frescos painted by him. Near the monument to Christopher Columbus along Paseo de Recoletos are sculptures Estatua de Rana de la Fortuna (Lucky Frog) and Botero’s Lady with Mirror. Further away is another Botero sculpture, the hand, while his El Rapto de Europa (The Kidnapping of Europe) is at Barajas airport. If you like churches you might like Catedral de la Almudena by the palace.

The bottom line is, if you don’t want to visit Madrid, stay elsewhere.

To clarify something Steven said, Madrid has multiple train stations. I believe he was referring to Atocha.

What is your plan for traveling from Seville to Porto? I assume you know that trains from Spain don't go to Portugal?

Lot’s of great options mentioned up thread. It depends on what interests you. After we toured Portugal for 2.5 weeks we flew to Madrid for 4 nights with a day trip to Toledo. We chose to take a Madrid walking tour with Ogo Tours at the beginning of our stay. This gave us the “lay of the land.” We took the train to Barcelona for 4 nights. We did two walking tours with Runner bean. Also beneficial like our tour in Madrid. We’ve never regretted walking tours when we travel. We didn’t do any day trips from Barcelona thinking we would go back to Spain sometime to explore more cities. That said if we had known then we might have enjoyed a day or overnight to Girona. I echo what was suggested already, “less is more.” Enjoy your planning!