I have 1" spacers on the rear and haven't noticed a difference in ride quality loaded or unloaded.

 

I used to have the 3/4 inch spacer from Top Gun Customz with the Airlift airbags in the rear. I did not notice any difference in the ride and when I towed my boat I aired up the bags and the rear didn't sag as bad. When I took the rear spacer out(I took the whole lift out because my travel to work changed drastically) I left the Airbags in, I haven't towed lately but I do keep the psi at 5-7 psi.

 

The ride won't change, as you said yourself, the spring rate isn't changing, so the ride won't change.

 

The spring rate is not changing but the pressure against the rear suspension is. The same amount of weight will produce the same amount of drop in the end but at uncompressed ride height the suspension is in a different location.

Its the same thing that everyone who throws a budget boost on a coil spring Jeep experiences. Nothing new, just what happens when you do a lift the cheap way.