If you wanted to add a rear ARB then you'd have to soften the rear springs to keep the dynamic wheel rate similar to stock. It would slightly change the character and ride quality of the car but not really the overall balance.
FWIW, when I modded my Miata and put coilovers on it I also removed the rear ARB to keep the ratio of dynamic wheel rates front to rear similar to stock. The car handled fantastic...no, it handled amazing. It's not about ARB or not, it's about dynamic wheel rates, roll centers, scrub radii, and tire choice [in a nutshell].
'07 Exige S270 :: Aspen White ::
"This is like O. Henry and Alanis Morissette had a baby and named it "this exact situation"."
Sterling Mallory Archer