Basically, the question is this: Are people reading the book for your writing, or for your ideas?
If it's for your writing (say, if you're a fiction author) then you should probably write it yourself. It'd be disingenuous not to.
If they're interested in your ideas (which is the case with most Kindle non-fiction books), then what's important is that your ideas aren't lost. That doesn't mean ghostwriting is fine, only that you need to find an efficient way to get your ideas out without wasting your time writing.
Basically, the process I use is to outline the book myself, sit down with a microphone, and talk through the entire book (basically recording a really rough draft of the audiobook straight from the outline). Then I transcribe it, and then hire a "writer" to work from the transcription to the finished text. That way it's high quality and maintains my ideas, but I don't have to do all the work of typing.
I wrote a book that breaks down the process in a bit more detail (especially the process of outlining, how to record effectively, how to find that editor, etc.), but basically what I said above is all you really need to know.
Here's the link if you want to check it out: www.amazon.com/Book-Box-Method-Quickly-Easily-ebook/dp/B014EUTYGM/