For full time writers, market potential is important. We do have to make a living. We also want to enjoy what we do. We've covered this a lot in other places. Mostly we make sure we know where the book is going.
Some collaborations work better than others.
They are best if the writers are equals or nearly so. Since I have readers from the science fiction, computer, education, and general science readerships, and several books have been best sellers, I'm not sure there is any answer to this. I don't dumb down what I write. I may explain things because not everyone who reads books has a general science education, and many are younger people, but I assume my readers are intelligent. I presume there will be other language editions of the book after it is out.