The subject of spirituality has long been controversial among atheists. Some argue that no self-respecting atheist should talk about spirituality because it implies supernatural entities of some sort. Perhaps they do not realize that not all atheists are metaphysical naturalists. Other atheists are determined to convince us that spirituality is good for everyone and that atheists should embrace secular forms of spirituality. They may forget that their own needs or desires for what they call spirituality are not universal and that some atheists find little use for spirituality of any form.
I recently watched one of the many YouTube videos available of Dan Barker's "Losing Faith in Faith" tour. I don't recall exactly which one it was, but I'd guess that they are similar enough that it probably doesn't matter. During this particular performance, Barker mentioned that some atheists who were not former evangelical Christians like him probably have a difficult time understanding the nature of the spiritual experiences evangelicals have. He drew a contrast between himself and Richard Dawkins, Christopher Hitchens, and Daniel Dennett in this respect.
Barker explained that some people (like him) have had all of the most intense spiritual experiences evangelical Christians describe and that this puts them in a position to understand evangelicals in a different way than the rest of us. I think he's right about that. Like Dawkins, Hitchens, and Dennett, I have never had spiritual experiences I associated with supernatural entities. I've had secular experiences that some might associate with spirituality, not all of which were drug induced. But I've never felt the presence of gods, been filled with "holy" spirits of any sort, or had the experience of feeling like my prayers received any sort of response. My attempts to understand the evangelical Christians have all been from the outside.
The experiences of so-called secular spirituality might be similar enough to religious forms of spirituality that they can promote understanding, and they might not. I have no way of knowing how similar the feelings of awe, transcendence, or oneness with all living creatures I've experienced at various times are with the spiritual experiences religious believers describe. The best I can do is to say that the way the experiences felt to me and how I described them afterward seemed very close from what I have heard from religious believers but without the explicitly religious connotations. My guess is that the primary difference boils down to how the experiences are interpreted in our minds, but this is only a guess.
I think Barker's experiences as a bible-believing evangelical Christian are one of the things that make him interesting. If we want to better understand something that seems extremely foreign to some of us (e.g., evangelical Christianity), it can be helpful to hear from others who have far greater familiarity with it. Individuals with this background, like Barker, can help us get a glimpse of what this is like from the inside.
As for the question of whether atheists should be promoting secular spirituality or opposing it, I'll take neither option. In my opinion, the question of whether spirituality of any sort is worthwhile is one that will have to be answered by each of us for ourselves. There have been periods in my life where secular spirituality was important to me, not so important that I would have tried to convince others that they should seek them out but still important. I have not been in one of these periods for several years now. At present, I don't have much interest in seeking such experiences. I have even less interest in trying to discourage anybody else from doing so.
If secular spirituality is important to you and you find it valuable to cultivate spiritual experiences, I say go for it. Pursue those goals while remembering that many atheists do not share these interests. If secular spirituality is not something you are interested in and you find little point in the pursuit of spiritual experiences, I say that's perfectly fine. Steer clear of such things if you prefer, but remember that many atheists do value secular spirituality. As far as I'm concerned, the only right answer when it comes to secular spirituality is what you decide is right for you.
If you are interested in the subject of secular spirituality, you may be interested in Sam Harris' new book, Waking Up: A Guide to Spirituality Without Religion.