Whenever I hear, "spiritual, not religious" I detect a huckster, one way or another. Give me an out-and-out non-religious non-spiritual dyed in the wool atheist god-hater over anyone trying to sell a "spiritual not religious" "program," or one of those fundamentalist Christians who want to pretend they're not fundamentalist Christians so they can make a convert
Why the fuss? Aren't there really people who are spiritual, not religious, just like there's martinis that are shaken, not stirred? Ah, no.
The reason is because there are definitions in the dictionary that fit religious as opposed to spiritual not religious, and those definitions comport with how I use the word "religion" or "religious" and how the words are commonly used. You can read on line all about cult-speak and how cults invent their own languages and all that, and to some extent that line of thinking's false because any sufficiently complex body of concepts is going to have jargon in it just to avoid making expositions of itself unwieldy. But to some extent there's truth in that, if only because people often want to bullshit themselves into thinking they're not bullshitting themselves. From a Buddhist point of view, it's that attachment thingy, and some Buddhists have it too, I would posit.
OK, so we're talking religious paths.
I am an applied scientist by training; an engineer who specializes in the research and development of communication systems. Many religious folks often don't realize or don't like that what science does is applied phenomenology. We don't do first causes, and this is especially true for engineering. The underlying cause of noise in a communication system, though often interference of man made or natural objects or beings, or due to remnants of the Big Bang, is irrelevant to the desgin of the system; its mathematical characterization is devoid of any unique "primary" or "first" expression (one of the beauties of probability and measure theory is the ability of the theory to express an encompassing "bracketing" this way). And even to a theoretical physicist studying the Big Bang, those phenomena that are not able to be observed, even by inference, are irrelevant to his studies. So Mr. First Cause can't get out of his brackets, and whether you're an Evangelical Protestant or a Hindu or Muslim or Atheist or Buddhist, a competent scientist will not try to peddle metaphysics as physics or any other branch of science.
In a sense, Buddhism is very scientific because it's observation oriented (i.e., mindfulness), but on the other hand, it is a great disservice to both science and Buddhism to say that one predicts the other, or that one is enclosed in the other or some such hooh-hah. They don't. They're different systems of thought, ultimately, though both involve some degree of observation, or recognize limits to which observation can be used. So to a certain extent I have to be put down in the "nonoverlapping magisteria" category of people in this side of the debate, though my argument, I think, is not from any deep metaphysics but from the fact that I don't find much use in traipsing down lines of thought like that. I don't want - yet - science to influence the core of my practice and vice versa. There's a reason my Ph.D. advisor was not a roshi and my Zen "teacher" is not a Ph.D. in engineering, and if I were ever to wear both hats I'd want to keep these things relatively separate because I think it's a bit arrogant and self centered to declare there are universal ways of combining these. Or not.
All of that said, I have a standing idea kicking back in my head to ask P.Z. Myers or Richard Dawkins about how to instill disciplined ethical behavior from a naturalist viewpoint. I admire the wit of the men and their principled and passionate lack of reverence for monotheistic religions, but I do think training, the practice of skill and discipline, and those aspects of a religion are not only useful, but damn near essential to live well in the healthiest sense of the word, and despite the chuckling I get from Myers and Dawkins, this aspect remains in my mind. It's telling in Dawkins' book that religions like Buddhism are ignored - or that others relegate Buddhism to "philosophy" as a way of saying "I don't mean your religion."
But...it is a religion. It's skills and rituals and practices and ethical guidelines and even a (near) metaphysic about the nature of beings, Being and so forth.
Even if the metaphysic is wrong, pragmatically, doesn't the skill produce better people? It would seem to be so for Buddhists: we don't get divorced compared to people in other religions, we're healthier, we tend to stay out of prison, and so forth, according to statistics I've read, but won't source due to time limitations. We're less stressed out, though sometimes my wife would dispute that with me.
In short, there's reasons for religions that aren't entirely bad, and science should be science and religion should be religion. But try to avoid junk science and junk religion, and without being disrepsectful of anyone in particular, we must submit that there is junk religion out there.