Barcelona's premium options mostly buy access and timing rather than luxury. That is a useful distinction, because timing is the scarcest thing in a city at capacity.
Worth the premium
The first slot at the Sagrada Família. The basilica's interior is about light through coloured glass, and the morning eastern light — blues and greens through the nave — is the strongest effect the building has.
It is also quieter, which matters in a space that gets very full.
A concert at the Palau de la Música Catalana. The hall has an inverted stained-glass skylight hanging over the auditorium and was built to be experienced with music in it.
Tickets for smaller recitals are often modestly priced. This is the best-value premium experience in Barcelona and it beats the daytime guided tour comfortably.
An evening at the Hospital de Sant Pau when it hosts events — the Domènech i Montaner complex lit at night, with a fraction of the visitors any Gaudí site has.
Depends
Private Gaudí tours. The value is coordination — a guide who sequences Casa Batlló, La Pedrera and the Sagrada Família to avoid the worst hours, and who explains the structural ideas rather than repeating anecdotes.
The buildings are the same buildings. Whether the sequencing is worth several hundred euros depends on how much your time is worth to you.
Tower access at the Sagrada Família — a separate ticket, a lift up and stairs down, and a view along the spires. Good, and not essential.
Rooftop and terrace access at La Pedrera, which is where the famous chimney sculptures are and is included in some tickets and not others. Check which.
The food end
Barcelona has a dense high-end scene and it books like any major food city — weeks to months for the well-known tasting menus, with some releasing tables on a fixed schedule.
The more interesting observation: the gap in quality between a €200 tasting menu and a €40 meal at a good neighbourhood restaurant in Gràcia or Sant Antoni is smaller in Barcelona than in most cities. Those need a day or two of notice, not months.
Market bars — at Santa Caterina or Sant Antoni rather than the tourist-priced Boqueria — serve exceptional food at counter prices.
Not worth it
Skip-the-line resales of standard timed tickets at a premium. Book direct with the site.
Flamenco dinner shows. Flamenco is Andalusian rather than Catalan, and the Barcelona versions are staged for visitors. If you want it, see it in Seville or Jerez.
Hop-on-hop-off buses in a city with a good metro.
The free things that beat paid ones
MNAC's Romanesque frescoes — wall paintings cut from Pyrenean churches and reinstalled in reconstructed apses. One of the most important medieval collections anywhere, and rarely busy. Free on some Sundays.
Santa Maria del Mar, a fourteenth-century church of extraordinary austerity, free outside guided hours.
The Gothic Quarter and El Born on foot.
Bunkers del Carmel, a former anti-aircraft position with the best free view over the city.
Practical
Book everything Gaudí as soon as dates are fixed. Walk into everything else.
Off-season — November to March — the timing premium largely disappears, because there is no queue to skip.