Some extra notes:
At the local 4WheelParts, I was able to handle and measure some spacers to determine that ones for the Wrangler TJ looked dimensionally perfect for the rear lower spring cup on my Rav.
I bought their .75" spacers which will lift the vehicle ~1.25". I took some more measurements today of various suspension components, and measured ride height before and after a scaled weight of 120lbs in the cargo area. From there, I have estimated the rear coil spring rate at ~200lb/in. (It took 120lb to drop the rear wheel wells .625", which gives a combined effective rate of 200lb/in. The coils sit 12.5" from the control arm pivot, and the center of the tire is around 25" from the pivot, giving a 1:2 mechanical disadvantage. Thus, each coil is applging twice the force as is experienced at the tire, or ~200lb/in per coil).
I am about .75" lower than stock with the weight (including the hitch, which I didn't remove) so this lift should put me about .5" above stock height (about 9.5" rear ground clearance with my larger tires). Thus, it would take another ~100lbs to sit back at stock height.
From here, basically every 200lb over the rear axle will drop it another inch. So, in all, for normal outdoor uses, with my dogs (75lb), wife (125lb, or about 65lb over the axle), kid (about 50lb) and maybe a cooler and some extra gear, I'd be looking at another ~250lb over the rear axle, which would sit me around .75" below stock, or right where I am now. I am okay with that :) .
I don't have time to do the work before I leave again next Monday, so I am paying a shop to do it tomorrow. I'll push results then.