am I doing NLP without knowing it?
I think you are, Tom! Everyone is - running programs and patterns, that either work for them (to have positive results) or not. NLP (in a super-tiny nutshell) makes you aware of those programs and shows you how to run the good programs instead (and how to stop running the ones that aren't so beneficial for you).
Michael's books are full of NLP, but you're right, just today I noticed again how he almost never mentions it. They are also full of spirituality and yet he doesn't really mention it. Smart, eh? Keeps the audience large and doesn't exclude anyone
On the other hand, that is what makes him "speak our language", plus the humor, which results in an entertaining and educating read.
I have done the NLP practitioner course, and I fully intended to do the Master practitioner as well, but I have noticed, that knowing what I've learned on the practioner is completely sufficient for me right now.
Maybe you don't have to do a practioner course, but i would definitely recommend an "Introduction to NLP" course or something. The very least you will get out of it is understanding yourself better (you might have quite some a-ha moments). And it helps you to get along better with other people and accept their way of seeing the world. All with scientific/psychological reasons and explanations.
If you're a spiritual person, you might notice lots of things that are overlapping - which can be explained both scientifically and spiritually (i.e. why you should always focus on what you want, rather than what you don't want).
I do not "practice" NLP, at least not consciously and I'm certainly no expert at it, but I do notice that the knowledge of the practitioner course is in me and I benefit from it everytime I need to explain something more thoroughly (when coaching people in communication skills for example) or give them just a little more information than what another trainer/coach could have given them.
So, if you're doing some self exploration, I would definitely suggest to look into NLP. I think some training institutes offer tasters for free, maybe you can find some in your area. An evening workshop or something. That's what I did, before I took any courses, I think.
Of course there are also books, but I've never heard anyone recommending a book in order to learn NLP. It's something you have to do live. You can read the books afterwards. I was sitting next to someone who said to me half way into the (7 day) course, "Now I finally understand the NLP books I've read!"