Bolded the not-to-be-missed.
Hotel: The el Jardin. HIGHLY recommended. Small rooms and showers that flood the bathroom floor, but clean and neat as a pin. Beds are heavenly comfortable with crisp sheets. Housekeeping staff quiet, efficient and friendly. Front desk staff helpful with bookings, directions, etc. I hated the Ramblas so getting to and from the hotel was not fun, but it is on the quiet Plaza Sant Josep Oriol which goes silent in the evening and has artisan markets on weekends. Get a room with a petite balcony that looks out on the church square, then enjoy the bells. Breakfast included; simple but sufficient. Very inexpensive and a 10% discount for paying cash. RS says you are paying for the location; I disagree. I would have paid more for a different location. But I was happy to pay for the quiet, the clean, and the service.
Ate at: El Quatre Gats--historically and architecturally intriguing, good food. The front tapas bar is a different world from fancier the back restaurant; try both. I found the RS-recommended tapas bars on the Plaza Sant Josep Oriol (Bar del Pi, El Drac de Sant Jordi) universally awful--the food was dried out and service non-existent. His recommendation of La Rita in Eixample needs to be updated: their lunch was 20 Euros, not 11, and service was spotty. My favorite meal was actually the little local bars in Barri Gotic--no frills, no English, no other tourists.
See: The HOHO was worth the price. We saw parts of Barcelona we would have missed--neighborhoods, hillside views, parks--along with famous spots we could return to. The Sagrada Familia is stupendous. Whether you are religious or not, this is a sacred space and glorious art. Plan several hours; advance tickets a must. See the attached school too, but avoid the over-priced and over-packed gift store which will kill your peaceful buzz. Park Guell is a monumental walk uphill from where the HOHO bus stops; don't attempt it on a hot day. Barcelona Cathedral is nestled into the city tightly, like Catholicism. During the festival of St. John, we saw the "gigantes" and the long, slow trek of the faithful (a rather frightening group of velvet-clad men and formidable old women), with reliquary. The Ramblas is dirty, crowded and awful; it's pick-pocket paradise--avoid, avoid, avoid. I was in Barcelona in 1974 when this was a tree-lined haven; very sad. The side streets are nicer; like Venice, easy to lose one's way. Find the Orwell piazza. Take a boat around the harbor for a different perspective and cool breezes. The Church of Santa Anna cloister is welcome on a hot day. The Palace of Catalan Music is a Modernista gem; see a show (Guitarra Espanola Flamenca highly recommended). The Block of Discord is worth a ride-by on the HOHO, but don't tour unless you are there in the off-season. RS walks are great.
What to buy: Leather belts. There are dozens of places; find one where the leather worker is on site and will build your belt as you wait--better quality and the high price will more likely go to the craftsperson.
Travel: Flew in on Iberian Air--a little slap-dash but has very nice staff. Left on the GNV ferry to Genoa. I hate flying and decided to see if this was an alternative to a really long train ride. It is. The cost was far less and included (poor quality cafeteria) meals and a tidy stateroom with a window, comfy beds, clean sheets, and a decent-size bathroom. Be forewarned: it is also a primary route from Morocco for trucks and truck drivers who spend the trip chain smoking and playing cards in the public areas. Large Muslim families also abound, with men who control their women but not their children (who ran up and down the halls until the wee hours of the morning). If you find the cultural aspect interesting, good and well. If screaming children and covered women make you uncomfortable, take the train. Very few tourists, though, and easy to board.