Buy the Cal-Tracs this year, run them with your /6 springs, they will work fine with them. Save your money next summer and upgrade your springs next winter if you want. The biggest thing Cal-Tracs did for my car was make it more 60' consistent.
There have been quality issues over the last 10 or so years with the new SS springs. Plus they make the car look like something from the mid late 70's with the rear end jacked way up.