First of all, let me say that none of this was directed at you specifically, especially not what I said about reading scientific papers, as I'm already aware of what you do for a living. You seem to have taken it that way, particularly by ending your post the way you did. But I will ask you this, do you think people who have never read a scientific paper or have any background knowledge of these subjects are going to simply comprehend what was written in the way that was intended? Even if they "get the gist of it," the assumption that it holds up under these specific circumstances is simply one that can't be made. The entire paper has to be read for more than just the results of the abstract. There are too many variables in these two studies to assume we are all just imagining that it works.
But to circumvent a debate that I'm not about to have, many growers have used coffee treatments and found evidence that it works. For some plants, no, it doesn't do much, but for Nepenthes and a few others, it works very well. This is all qualitative, as nobody here (at least, not me) cares enough to run a formal experiment in order to disprove it. I'm not going to run statistical analyses, spend months of my life, and petition to use lab resources on this. But you definitely could, since you do work in a greenhouse where I'm sure space for control plants is ample. In fact, I'd love to see it. Maybe you could even have undergrads do the tedious work for you. And, you already seem to have the questions laid out nicely.
Again, I'd rather not go down your list, but my comments on acidification were not really worded in a way that would allow you to assume that this is what I feel is causing the "good effects." I feel that it may have something to do with it, but I never said this is solely what causes it, nor would I be so presumptuous as to pretend to know.
I appreciate the studies, I found them very informative, and I'm not saying they're wrong, but saying you have to "put this coffee thing to bed" comes off as a specious statement when considering the diversity of the plant kingdom. I doubt even the authors of those two papers would try to assert that compounds found in coffee would have definitive allelopathic effects on all plant life, especially those that are not even closely related to the test plants, at least to the point of noticeably inhibiting their growth.