I think night vision / thermals are more pay to win than paying more for airsoft guns or ammo. If you gave me £2000 and £200 to put together two separate airsoft guns, the £2000 will undoubtedly be nicer, but the £200 will be more than competitive. Good quality NVGs or even mediocre thermals give a significant leg up over the guy using a white light and showing everyone where he is every time he wants to see anything. Yes, a skilled player with no NVGs will probably get the better of a poor player with NVGs, but a skilled player with NVGs will do far more damage at night than a skilled player with a good gun during the day, which is much easier to overcome with cheaper gear.
Someone rocks up with a set of quad nods, some sort of amazing analogue NVGs that would require a mortgage to afford then you're generally screwed. Even trying to blind them with white light is difficult with all their fancy sensors and automatic adjustments, but most people will use either cheaper analogue or even digital NVGs that you can totally blind and potentially even damage with a bright white light; I don't even think I'd feel that bad if it happened to someone, in the same way that if someone brings an unprotected red dot that gets shot out, it was their choice to bring it to a game of BB wars where there is a not-insignificant chance of damage and so the fault lies with them. Sure, if someone is purposefully going point blank and shining a bright light directly into the tubes then that's called being a cunt, but if someone happens to be shining white light that hits the NVG player and damages the tubes, then that's just a hazard that you have to be aware of as an NVG user, much in the same way that you should always run a protective cap on a red dot sight to mitigate the possibility of it being shot out.
However, thermal is definitely a cheat code. There are ways to mitigate it, but hiding from even a cheap thermal optic is incredibly difficult. I've been tempted to pick up a cheap thermal monocular myself for getting into milsims and using it as a spotting device, then relying on short bursts of white light for shooting.
I'm generally on the side of having no NVG games, even as someone who is getting more into milsims and getting a thermal monocular for myself. I am also a Driver Wood player and I actually chatted with one of the marshalls about it and the whole reason they don't do NVG games is because they just didn't pull in the numbers. What they observed is that the people who rocked up with NVGs and thermals generally dominated (obviously a small number of no NVG players still did fine, but the majority struggled) and it put people off, so their attendance absolutely plummeted over time as people without NVGs simply stopped showing up, and so as a business it made no sense to keep running them.
If you want to play a night game with NVGs, I'd recommend milsims. You'll be among many likeminded individuals there, and they do pull in the numbers.
(Asking for a friend - that friend being me) 
