Hi guys, I currently have a sport kit on tokico HP's. The struts are fairly new but the springs are going on something like 8 years...

My rear is starting to sag too much. I am looking for an easy way to raise the rear up a bit without spacers or making it any stiffer.

Would it be a horrible idea to buy a set of prolines and install only the rears? I would like to keep the front nice and low on the sportlines..

I am not tracking the car so I am not too* concerned about mixing spring rates unless its going to be way out of wack combing the two.

Your sagging rear might be due to blown or weak rear shocks. They are gas charged and can loose their charge resulting is less resistance in the rear. When the rear springs were installed did they remove the stock spring seat pad? or perhaps cut it down? The stock pad is like 2" thick, often people cut them down to get additional drop in the rear, you might just need new spring seat pads.

As far as mixing spring rates go, I have no idea what the rates for those kits are but generally you want a lower rate in the rear. If the rear rate is higher than the front it get very tail happy very fast. If the spring that's in there is collapsing the spring rate changes as it collapses.