Most adults reach a certain (not very old) age where they no longer have 20/20 near vision. Ask your doctor about it so you won't be surprised one birthday.
ok my father is 50 and needs reading glasses and still loves the iphone 4 display because of the resolution. It's not like good sized text on an ipad is going to be 3/10 the size on an iphone display, and since it is so crisp (only for retina display, not so true for the older ones) you can see smaller than you ever thought you could.
The subject does not shrink with the display, only FOV. If the sacrifice in FOV is really worth the worse battery (audio playback is as much as 40 hours!), cumbersome size and keyboard, impractical transport options (always needs a bag to be mobile), phone capabilities, camera, facetime capability, gyro, and plain simplicity (combine 3 devices into one; phone, media tablet, ipod), then the ipad is better for you.