It depends how often you use it. I used to use my unholy book all the time, and so it was worth the 16-18M I spent at the time to fill it.
I hardly touch the thing nowadays though, so I wish I could rip out the pages and sell them. Also, when I originally not an unholy book years ago it cost like 1M maximum to fill... so 22M is just ridiculous.
No the bonuses are not worth it, but i would take that 22m and maybe put it towards stats or botting funds to help increase the effectiveness of your pure