RS, it pleases me greatly when I find I've come to the same conclusions
as you.

I'm just finishing work on a cheap slow flier. It's a departure from
standard, at least for the wing, so I've overengineered the safety side
(BRS, 5 point harness and a pilot's parachute). But for
instrumentation, I'm minimal. Handheld GPS and com (since I'm in the
busy traffic of So Cal, I'm addicted to com)

EGT and CHT for the single cylender 2 stroke. RPM. Fuel level is
visible. Altimiter - So I can get a good idea of rate of climb.
Airspeed is a plastic tube with a red plastick floatie disk. That's
it.

OTOH, I have the Uber Panel in the expensive fast flier. Two missions,
two solutions.