It's odd, these festivals. I'd never go to Glastonbury; to me it's a four day hellish version of Later...
Likewise Download. Aah, I remember the old days, drive up, backstage parking, watching Motley Crue and Aerosmith from the side of the stage, proper bogs home and asleep in my own bed about 2.00am the next day. Now? Four days of bands with vocalists just clearing their throats. Nope.
When all this was fields, the events that got my attention were just 12 hours. It's difficult to fully quantify but take the old Monsters of Rock things at Donington. 70,000 people, one stage and (usually) seven or eight great bands. Now it's all multiple stages, dozens of bands no one has heard of etc.
The day long Donington has evolved, but the 1980s type event would now be supplanted as part of a tour itinerary (if this makes sense). It would be like Green Day just playing Wembley Stadium with a decent undercard, then this moving to the Manchester City stadium.