Nils Rostedt wrote...

Speaking of gliders, I wonder if any gliders have
an arrangement whereby both ailerons can be moved
in unison to a really high negative (up) angle,
in effect acting as spoilers or speedbrakes...

What you describe sounds like "crow" mixing,
where the flaps go down and the ailerons (both)
reflex up. It's still used in RC gliders, and
given that there are several powered airplanes
that use it or something similar I'd bet that
there are full-size gliders that use it as well.
There's also trailing edge reflex, where flaps
and ailerons all move *slightly* trailing edge up,
but not a lot, and that's for drag reduction in
cruise, not drag increase for approach. Some
full-size gliders use this as well.

Dave 'poor man's DLC' Hyde