I'm not the #1 Primavera superfan...there's another person here (who doesn't post anymore) who has been to Primavera since its inception.
When I went in 2009, I actually spent less money than what I spent at Coachella 07 because a.) you don't need a car, b.) hotels are cheaper. If you are undecided at this time, you can try to book your flight two or even a week in advance and see what you come up with. In 09, I booked a week prior to the fest and it was around $500 roundtrip.
Setting and weather are perfect. There are 6 stages and one beautiful auditorium that holds 3,000 people for select performances (MBV played one of their 2 shows in the auditorium when I went and this year it will be Sufjan Stevens, Mercury Rev, John Cale and more). There are also pre-shows/after-shows and that's included in the festival pass (this year it will be held at Poble Espanyol instead of the clubs) and there are also preshows at Parc Joan Miro (not sure if they are doing that this year).
I didn't get lucky last year as far as flights due to people flying to Barcelona (fares got too expensive) to avoid the volcano so I had to cancel hotel reservation. I'm going this year, though! (will be there 8 days total)
