Barelona will be way better than Valencia. There are seats that let you see huge amounts of the track, and all the granstands are open on friday, easy to break into on saturday, and plenty of free standing room on sunday.
In saying that i had grandstand tickets so it took some of the stress away from having to look for seating all the time
Beware of the journey there. Its about 2 hours long and took me a bus, two trains and a 45 min walk. Getting back will be even more hektik with 100,000 plus fans all trying to get back home aswell
Or fcuk it, monaco was awesome, do it again