I'm not sure about the usefulness of grouping the kind of vague spirituality and religion mentioned in the first paper with the discussions of meditation in the other papers. As the last paper argues, I also would think it would be worthwhile to distinguish different forms of meditation. My general understanding of the state of the literature was that studies of the benefits of "spirituality and religion" were all over the place (it being an incredibly vague category). I also was under the impression that there have been a lot of studies of meditation specifically, and that it was common for them to find substantial benefits, but that there remained controversy over why, over whether some methods were better than others, and over whether meditation was superior to relaxation exercises. I'm certainly interested in all of that research on meditation myself, but it seems to me to be in a different category from other kinds of "spirituality and religion" research.
I get papers cited at me, (the first is about "religion and spirituality", the rest about specific meditation disciplines) about but I can't tell whether they're well-done or not. I believe LessWrong is the ideal place to ask about this because there's a healthy combination of interest for self-improvement techniques and solid skepticism against quackery. I thought it would be a solid enough topic to merit its own thread rather than a discussion in Open Thread.