1. The bug is also present in the regular Android Kindle app. For instance, my Archos 43 minitablet has perfect font rendering in normal portrait (on the Archos display the RGB stripes run horizontally in portrait mode), but shows a bit of the bloom in landscape, only in the Kindle app.
2. As for brightness, I wish rooting weren't illegal! Then it might be an easy fix, just as it is on my Archos 43 ( for users outside the US where rooting without the manufacturer's permission may be legal, you can try my SuperDim app:
http://code.google.com/p/superdim )