Got to admit, I had no idea there were books on itchio until you pointed it out but, yeah, 9,310 of them in that section.
I suppose it just depends on whether you think maybe a couple of hours of your time to upload the pdf/ mobi/ thumbnail (or whatever) is worth it- and you've done most of this already.
As someone who's done both, I find promoting books even harder than video games, so I'd say it's worth doing anything you can- even if itchio is unlikely to be anyone's first choice as a book website.