Gaudi Sites in Barcelona

I have serious doubts about that pass, and I would take with a large grain of salt any other advice you found on the same website. You have to do the math. List the sights you definitely plan to see. Figure out how many days it will take to see them, not forgetting travel time and the necessity of lunch. Be sure the pass allows you to skip the ticket line. Do you still have to make a time-specific reservation? Will there be capacity limits on the number of pass-holders allowed to book a specific time? Will the times you want be available?

Keep in mind that big-city sightseeing passes like that are money-making vehicles for the companies putting them together. For that to work, the pass sort of needs to be a waste of money for a lot of travelers.

Places for which you must buy tickets in advance because of horrible ticket lines (and potential sellouts) are La Sagrada Familia, Parc Guell, Casa Mila/La Pedrera, Casa Batllo, the Picasso Museum (no Gaudi connection there) and the Palau de la Music Catalana (not Gaudi but a stunning modernista building, and the English tours can sell out). The Palau Guell ticket line is usually not as bad, but it would be smart to get that ticket in advance as well.

I don't know about the Camp Nou tour (soccer/futbol, not Gaudi).

I found the Casa Vincens interior rather disappointing (not many rooms to see, and not nearly as flamboyant as Casa Mila and Casa Batllo), but some other folks here recommend it. The exterior is worth observing for sure, but I don't know how much is visible without paying for entry.

The other Gaudi-related sights you can just walk up to.

Casa Amatller is pseudo-medieval and not designed by Gaudi. It's reasonably interesting. I don't remember a line there, but I think you have to take a tour, so some degree of prebooking is probably necessary.

You should check out the Ruta del Modernisme. There's a very well-priced package including an illustrated, soft-cover (but heavy!) guidebook, a map marking perhaps all the modernista buildings and a discount-coupon book. I think the discount is 15% or 20%. Unless something has changed, you can only get the discount if you buy a ticket at the ticket counter, which is totally impractical for the high-traffic places mentioned above, with the likely exception of Casa Vicens and the possible exception of Palau Guell. But as you know, there are other places to see. If you do manage to get inside all that are open, you should at least break even on purchase of the package, making the guidebook and map essentially free.

Ruta del Modernisme main webpage

Ruta del Modernisme guidebook and package

Each person in your group needs a discount booklet, but that can be purchased for €5. This is a very good deal, though the discounts themselves are not large.

The second link includes the addresses at which you can buy the RdM package. Only the first is in downtown Barcelona, and it's only open Monday-Friday. When I went there in 2016, the fellow in the office didn't speak any English. I managed on the spur of the moment with my limited and rusty Spanish, but if you won't have a Spanish-speaker with you, it would be smart to print out the webpage at the second link above. Even though it's in English, the staffer should be able to figure out what you want if you draw a circle around the list of items. I don't remember whether paying by credit card was an option, though It seems likely.

The Recinte Modernista de Sant Pau complex (a former hospital) is a beautiful modernista site not by Gaudi. It's by the same architect who designed the Palau de la Musica. Highly recommended. You can walk up and buy a ticket for immediate entry.

The privately-run Modernism Museum is smallish and not cheap but interesting for decorative art. The MNAC has a good collection, too.

We did a full day Gaudi tour with Forever Barcelona working with the owner Marta. https://www.foreverbarcelona.com/ The entire day was planned and executed flawlessly. It was a long day but all of the logistics were planned so we could hit the sites in one day. It’s pricey but we found it was worth it. We also used her for a 1/2 tour of the old city our first morning which gave us a very good orientation. Highly recommended.

Barcelonan here. My two cents: while Gaudí was indeed a brilliant architect, there are plenty of other masterpieces to see in Barcelona. Some from the same time period but by other equally great architects such as Puig i Cadafalch or Domènec i Montaner, but also from other time periods such as the Roman remains of the original settlement or many magnificent medieval buildings scattered across different parts of the city, such as Monastir de Pedralbes.

I say this because, unless you have a very special interest in this specific architect, it seems you're going to overdose on Gaudinianism to such an extent that by the time you see the fourth house, everything is going to look the same to you. Moreover taking into account the fact you're packing your visits in four days only. Perhaps I would plan fewer Gaudí sites and intersperse some others to, in some way, have a break.