Not only do I like a bit of 'thinning' of plane icons via an opacity adjustment, for my 32" 2560 pixel wide display I use an 8 point font. I guess I prefer as much subtlety as I can impose without making readability *too* hard. A way of partly compensating for the 'cheating' of having labels in the sky.
It does go somewhere between no labels and obvious ones.
Moreover, some time ago I created/tweaked *map* icons similarly, making them simpler, smaller and partially transparent. I've ported those over, and made similar adjustments to others not formerly used in my old 4.08 game. I like being able to at least partly see the underlying map beneath the symbols, which is particularly useful where objects become more densely packed in busy scenarios. And plane formations/furballs are more easily assessed when they don't all lie practically under one big, opaque plane symbol.