If you want to contribute by adding new sentences, you could try to do a later chapter -- maybe Chapter 60 or something -- and see how it goes. The sentence writing itself is almost completely separated from studying. The difficulty that you'd run into by doing a later chapter is that there will be a lot of kanji the book assumes you already know, and will not give you the readings for them. Of course, you could get around this by using a dictionary, but...well, "tedious" would be an understatement.
Please feel free to contribute by proofreading. This is a very important stage that I haven't even begun to tackle yet. It needs to get done, and there's nobody better than someone who's going through the sentences for the first time in order to use them.
As an aside, for my study method, I highlight the target kanji in red (so that it stands out), and then my answer is the reading in hiragana. Usually, I read the entire sentence out loud. If I want to speed through my study session, though, I can quickly just look at the kanji
compound itself without focusing on the context of the sentence (ironic, given the series' title, I know...). Lately, I've been getting more strict with myself, and will fail a sentence if I can't read (or even more recently, recall the meaning of) any
of the kanji compounds in the sentence. It makes my reviews about 10-20% slower, though.
Yeah, I am really happy with this series, although I know that it's not perfect (no textbook can be). liosama brought up an interesting point -- s/he's using the book for readings but not focusing on the grammar. I think this works alright for KIC. You mentioned working through both Genki texts, which indicates to me that your grammar will be pretty low for KIC. If you don't already have a fair amount of grammar knowledge and you focus on grammar as well as reading, KIC will be difficult to get through. In this situation, KO would probably be better and faster for you. In my case, I had finished An Integrated Approach to Intermediate Japanese
(I think it's the next step after Genki II), and even then, the grammar in KIC was "comfortably new" for me.