I'm double vaccinated, reasonably low-risk, but one remove from a friend who's immunocompromised, so my risk assessment is a bit different from yours, but I'm definitely going to be doing things slightly differently this year. It's definitely not a great idea if your goal is to never get COVID, but if you've been missing music, and want to see a lot of it at low risk compared to doing a dozen indoor gigs, then EOTR is looking pretty good.
The ONS estimates roughly 1 in 75 people in the UK have COVID, which will almost all be Delta. It's significantly more transmissible than good ol' Alpha, definitely isn't stopped dead by vaccine, and there have been a few documented cases of outdoor walk-by infection without a mask, but a KN95 should take your risk right down. An hour in a packed tent without a mask seems like a bad idea to me unless the wind is fair whistling through it. Masked, I'll still think about where I'm standing, and look for a clear, better-ventilated area. I'm usually a barrier-hanger, so that's a convenient way to approximately halve exposure. Even in the outdoor areas, if people are packed, and it's a still night, I'll be tempted to pop a mask on or find somewhere else.
Toilets are the other big one, I think - giving the toilet door three or four big swings before going in seems like a decent way to do an air change, as well as having some fringe benefits, and I wouldn't go in after anyone who'd been coughing in there.
So yes, it's riskier than staying at home, but I'm going to take the precautions where I can, avoid/ignore any idiots (just like usual), and maybe spend a bit of my risk budget to get in a good spot for two or three acts. Then lateral flow test before I head home, and a bit of planning for the following few days in case I'm infectious but asymptomatic.
Final thought: be wary around Big Jeff - there's likely to be a larger than average pocket of still air just downwind of him, so give him some space...
