I would jump back to Geo Tracker rear springs, give those a try. They are quite a bit lighter and will drop your rear end an inch or so. We did a 4 link with GV rear springs on a Samurai and like you said they were to stiff. The owner had problems climbing up hills in 2 wheel drive due to the rear end just not squatting at all. We swapped over to some 2 door rear Tracker springs and it worked great. Also dropped it an inch or so.
Stock rear 2 door Tracker springs should be rated around 155, 4 door springs at around 175. Rear Vitara springs I believe are around 200, but the chart over at Low Range only lists GV.
You will get a bit of a lift with the add-a-leaf kit, can't tell you how much though as it varies per rig. I would give it a try first before spending money on shackles.