Mark Fisher wrote:

What is the view (especially of instructors and inspectors)
on spinning K13s within the non-aerobatic range of
the placard?

Gliders are usually certified in the utility category, to which JAR22 says:

JAR 22.3 Sailplane categories
(a) The Utility Category is limited to
sailplanes intended for normal soaring flight.
The following aerobatic manoeuvres may be
permitted if demonstrated during type
certification –
(1) spins;
(2) lazy eights, chandelles, stall turns
and steep turns;
(3) positive loops.

Now as the K13 has been certified well before JAR, this doesn't answer
your question. :-P

Stefan