Thanks very much, all. I like your versions, dobson & amtr_kid, much better than my original. Here's my second attempt:
Second version link
I think I'll try yet another one more along the lines of yours, though - I still have a tendency to end up with too much contrast...
I agree, and I have one comment to add: in my view, the reason the B&W versions fall short of your expectations may be that (so far), they don't reflect the quality of the light or the subtle tonal relationships of the original image.
IMO, you are right that your first attempts were too high-contrast. I think they were also too bright, overall. In the original (color) image, there is a lot of detail visibile in the high values. You need to make sure you don't lose that when you do your B&W conversion, even if that means that the final image ends up not containing anything that's truly "white" (in the level-255 sense of "white"). You may also want to find a way to express the subtle difference in value between the shaded and sunlit foreground elements (that difference is easily visible in the original image and somewhat lost in the conversions). Finally, to my eye, the tonal value of the sky seems to be too high in the B&W versions, which gives a different mood than the original capture.
The best advice I can give is to examine each channel individually and use the Channel Mixer (manually) to get the tonality that you want. You can adjust overall brightness and contrast after the fact. I'd also suggest that you consider burning and dodging local areas (AFTER B&W conversion) to really fine-tune the image. If you find the channel mixer painful to use (I often do), something like Convert-to-BW-Pro can be a winner, but you'll probably still need to make local adjustments.
I hope this helps. IMO, you have a very nice original image to work from.