Upgrades on Kindles have tended to be with slightly faster processors, slightly higher resolution. So sharper text. Also the back light has been more even with later Kindles.
Yes. . I bought one for my mother, hoping her 90year old eyesight could work with it.. the text in books just to small, however she was beyond learning any swipe gestures, so I gave it as a replacement for my wife's original kindle, and she is very very satisfied with it.....
I made the text on my Kindle bigger as I too found it rather small. I haven't got it with me at the moment but I am sure you would be able to fathom it out!