That's exactly my reason as well, the eyesight. I was in a Sony Store looking at the 4K TVs. Yes, it was very good, but the difference between that and Blu-ray, IMHO, was negligible. I'm in my 50s now and my eyesight will only continue to get worse as the years fly by.
The difference between HD and 4K is actually quite large. The problem is, unless you have a 70" TV, you can't see it.
4K will be amazing if you have a mansion and a private theater. Not so much for your standard living room HDTV. Hell, most TV's refresh rate probably isn't high enough, either.