But would I rather enjoy today the full effect of never having had the knots, in exchange for not having any? Once I asked the question that way the answer came back a resounding yes. I didn’t know how much it would matter, but the calculation wasn’t remotely close. I walked right past the pizza place and never stopped in there for a snack again.

I think the interesting bit here is not the comparison you made (it's described quite explicitly in more than one self-help work I know of), but that you transposed it to the past.

That is, you appear to have effectively said, "If I'd not taken action X all this time, I'd have result Y; would it have been worth it?"

I would expect this to increase the usefulness of the technique for people who view the past in an especially concrete way, and/or have difficulty thinking of the future in concrete terms.

In any case, the improved effectiveness you experienced is almost certainly due to this one bit (improved concrete construal counteracting the discounting effect of an abstract future) rather than to anything to do with TDT.

I think I shall try it myself on some things, and see what happens.