I have a Kindle and love it. I'm not sure the Wainwright guides would make for a good conversions.
The books are brilliant, but you often find the need to skip backwards and forwards in them when out on walks. Not so easy to do on a Kindle.
As for the drawings and stuff, they would be black and white to greyscale and should go across well, though you would lose the red line introduced in the revised versions.
As for the pricing being set by Amazon. They aren't. Amazon made it clearly that the publishers have forced agency model pricing on them (which was previously outlawed on physical books). I complained, as did many others, to the OFT and the whole ebook industry is now under investigation for price-fixing.