Many thanks to everyone for the advice, both on this thread and via PM (cheers Pincher). I would normally buy books and do research online, but it was essentially a work trip to speak at a Conference, and I only decided to go out a day early and take 'auntie' at fairly short notice.
In summary, we arrived late Friday night. Late, but not late enough to walk down Las Ramblas and sit in a tapas bar with some Patatas Bravas, Chorizo, Manchego, Jamon Iberico and Cerveza 'Muy Grande' til 3am
Out early on saturday, walked to Sagrada Familia, metro to Catalunya, down Las Ramblas and Bari Gotic. Harbour, cable car, Mont Juiic, olympic stadium, fountains and metro back to Passeig de Gracia where the Hotel was for a beer on the rooftop bar before dinner at the Gallery Hotel (the start of the conference).
The view from our hotel's rooftop bar was stunning. You can see the whole city and the close up view of Sagrada Familia from there is probably better than at ground level.
Auntie got a bus tour on Sunday with some of the other conference WAGS and we had a great meal at El Principal (restaurant just off Passeig de Gracia) on Sunday night before a few (free!) beers back at the hotel. Had to decline the early hours Salsa dancing club visit though as I was speaking to 100 odd accountants and lawyers on Monday morning, many of whom don't speak English as their first language.
Monday morning was shopping for Auntie while I did my presentations, then a bunch of us wandered back down Las Ramblas for a last look round Bari Gotic, the Mercato and have a cold beer and (fantastic) hot Paella on one of the tables round the outside of the market.
Wonderful city, perfect weather and great advice from the FISO community.
Muchas gracias a mis amigos en FISO