The free "AIP" plates were mostly designed for A4 and when reduced to the A5 size (at which Jepp, Aerad etc plates are published, and usually printed) they are a bit too small to read. Some of the text is especially small. I did a lot of messing around with this a while ago and concluded that 1024 pixels (along the long axis of the plate) is the minimum at which the AIP plates are legible - reading glasses or not.
The Kindle DX is 1200x824, which is pretty much indistinguishable from your 1024 pixels. The problem is that the pixel density is sufficiently high that the physical size is small, which means that no matter how high the resolution, you need good close vision to read an originally A4 plate like the UK AIP ones.
The flat directory structure is indeed a drawback.