A year or two ago, there were people suggesting that low spins, say
below 1500 agl, were an important training exercise since they let the
student experience the shock of a canopy full of earth coming on
quickly. By having experienced this, the pilot would be able to react
more quickly to the accidental stall/spin in the pattern and thus
effect a faster, safer recovery.

Are you saying that you agree with this, that you practice it, and
that it has become common practice in the UK?

(You note that you start your training at 3000 agl, then imply that
once the student is acclimated, you bring the entry altitude down.)