[sperry]

IMO, the benefit of SS lines is more directly related to the quality of the equipment you're attaching them to rather than the (lack of) quality of the old lines that are coming off. Certainly replacing crappy worn out lines with SS lines will make a difference, but not as much of a difference if the car still has crappy calipers. Basically, the lines have to be the weak link in the braking stiffness chain for SS line to be noticeable.

For example, I added SS lines to my stock WRX brakes and there was a noticeable improvement because the stock WRX sliding calipers aren't all that bad, even though the lines that came off the WRX weren't all that worn out. But adding SS lines to my SVX made virtually no difference in feel because the SVX's sliding calipers are so sloppy to begin with, even though the lines getting replaced were worn to the point of leaking.

My guess is that putting SS lines on the 4-pot WRX calipers will result in more positive feel, even if the existing rubber lines are relatively new. But I'll point out that the benefits of better feel due to SS lines are not all that huge unless you're really pushing the car to the limits on a regular basis. Certainly SS lines on a street only driven car are only going to be "better" in that the lines will resist damage better than the rubber ones. You really won't be able to make better use of the brakes because of the SS lines on the street.