Re: GTV/Spider - Powerflex Or Not ?
Overall the powerflex upgrade is worth it. If you replace all fourteen bushes on the rear the handling is more secure and you can place the car with more confidence through the bends. However, I would suggest a damper/spring upgrade at the same time to complement this improvement. Replacing one without the other will not give you the degree of surety you may be after. It all depends on how far you wish to go.
However, with the decision to replace all fourteen rear bushes, there are caveats. Without going into too much detail, I would suggest that the set of six bushes on the trailing arms are the best ones to replace, the outer ones especially so. Things get more difficult with the springpan bushes. If money were no object, I would suggest replacing your TS springpan arms with the 3.0 V6 ones, as these are rose-jointed (the later JTS cars I believe are rose jointed also). Again, it all depends how far you wish to go.