Tom,
"Does that mean Vy is closer to 250+ ?? "
That's what I'd expect for this class of aircraft.
"I would expect that a slight reduction in induced drag at the lower weight would contibute just a little more RC, no?"
Yes although as you say: just a little more.
"Not sure, since even at LW I'm not really "going faster", I'm still at the same airspeed. Is your following AOA and "napkin" result still valid?"
Yes it is, should have said same airspeed.
"That's interesting, can it really be that simple?"
Yes. The real equation is sin(gamma)=(T-D-aW)/W so assuming T(thrust) D(drag) and a(longitudinal acceleration to maintain constant indicated speed) are all unchanged or negligible in the case of a, we get sin(gamma1)=constant/W1 or sin(gamma1)/sin(gamma2)=W2/W1 in other words the climb gradient increases by the ratio of weights.
Of course a is not really negligible and D is a bit smaller but the approximation gives a good idea of the change as long as we deal with similar speeds.