but I mourn the loss of 'the proof of the pudding is in the eating', for the relatively meaningless 'the proof's in the pudding'.

I agree with you that some changes are destructive, and therefore to be deplored. However, I rather like your example - it tends to increase the meaning of the old saw, rather than diminish it. One can read so much more into that gnomic adaptation of the old saw.
(e.g., "I dropped my new book whilst I was correcting it in the kitchen. Now the proof is in the pudding." )

I like the one that I overheard a colleague use today;
"Well, we aren't dragging our wheels over this one."
As so few people use their feet enough to drag them, these days, the vehicular reference is particularly apt. It also has the connotation of going off course.

However, I do have to admit to moments of irritation when I hear well-loved phrases being put through the mangle.