From what I've been told re: BER on tomatoes, yes, it seems to be linked. However, I have found that I do have the problem with other veggies that are known to develop the issue, and it does correct when Ca is added. And I generally absolutely agree with you about the worms, but one of my gardening areas was built on top of a large sand filter (part of our engineered septic system, and the ONLY level area outside our home and garage itself), and that's encased in concrete, so I don't think worms are easily able to get into those particular beds. That's why I 'rescue' the worms that always erupt after a rain and throw them in those particular beds.
I've got a fraction of the time on my land you have on yours, I'm still working as best I can to get real soil built up on top of or in my clay. Mine doesn't just contain clay, it IS clay, pretty much nothing but.