I don't know if this will work for you, since you probably print the hard copies from the PDF, but something that would make the book much more readable on eReaders would be to significantly reduce the margins. For example, I've been reading my copy on my NookColor, and it works great. But with a 7" screen the text is very small and the margins are really big. Luckily the NC has a the same resolution as the iPad, so it's still readable. But I can't imagine trying to read it full page on a tablet with a lower pixel density.
Since in electronic format (on any screen) doesn't require a gutter for the center of the pages, you could chop about 75% off the margins all around and instantly give your PDF readers a larger, easier to read presentation.
I don't know what program you are doing your layout in, but you could even do it quickly and easily in Acrobat Pro by cropping the pages (leaving out the title pages, since they have full page graphics).
Anyway, just a suggestion :)