Rather than thinking in terms of middle ground, think in terms of making the inevitable easier on your kids - because there certainly are things in life that are... if not inevitable then at least major limits in life, and it goes a long way to look for ways to make it easier for kids to navigate those.
So, in terms of taking a 4yo someplace they're going to be bored and frustrated when they'd rather be home, I'd look for ways to make the experience less onerous on the 4yo. Pack fun things in the car. Plan to bring special snacks and activities that are all about the 4yo - stop for ice cream, maybe, or get a bunch of glow sticks and run around the parking lot in the dark. Get a new video game for the occasion to play in the car. Treat it like... going to the doctor's office - how could you make the experience less unpleasant for everyone?
All that being said, it's good to keep in mind that some kids have a harder time with transitions than others - and 3-5yos often find transitions hard. You can try to soften them, but it's worth asking "is it actually worth bringing a little kid to something like this?" I mean, no-one enjoys a bored, frustrated little kid, and having one along can really ruin an experience for everyone. That's not a "discipline" thing, that's real life with little kids. They don't Belong everywhere. So it's not really productive to put them through a hard transition for something that's just going to suck.
For something like the event, then, it would have been helpful to try and brainstorm ways for the 4yo to get to see the big event without having to be in a place that's really, really not designed for young children... like maybe live streaming, or making a video to watch at home. Or just taking lots of pictures. Then the experience could be about the kid to whom the event really matters, rather than the needs of the 4yo, and there'd be mementos.
It takes some practice to get used to dealing with kid stuff like that, thinking and planning ahead with realistic expectations, but it's sooooooo worthwhile because making things easier on your kids makes it easier for the whole family.