350 euros seems like an excessive price to me... obviously, times have changed, but it's clear that a large part of that expense is necessary to book big names in the industry. I've always been a strong advocate for headliners at Primavera Sound being something completely secondary, but inevitably, they impact other aspects and features of the festival.
It becomes difficult to pay those prices when, for the most part, you want to see smaller artists that you can access at much lower prices in other festivals or on their own tours
I think you're being exceptionally generous there (albeit as I said I only saw the last 3-4 songs, it may have been much busier earlier on). My guess at the time was about 10k, and with reflection I think I was probably a little on the high side.
Why? If the system fails then anything could happen, but if it performs surely they will have at least the same capacity to process sales as before? It may even be quicker.