You'll see, it'll do perfectly in a couple of decades. Most people wear glasses nowadays, and those who don't will at some point in the future.
Nope, I'm "old" and wear glasses and my small 4k monitor (~250dpi) was a significant improvement.
Actually, my eyes are more sensitive to low resolution as they get worse. The blurry of the text compounds with natural blurriness of eyes.
Wearing glasses doesn't reduce the need or desire for higher resolution monitors. Maybe uncorrectable vision problems do, but if your glasses get your eyes close to 20/20, you'll benefit from higher resolution just like people with natural 20/20 vision.
And as another poster pointed out, the blurriness of the screen may compound with the natural blurriness of uncorrectable vision loss.
Depends on the usage I guess.
The larger the screen, the further away you stand.
I have a 2560x1440 32" monitor with a <100dpi. It's great for text editing (I use a bitmap font). For other use, I would love 5k :)