I have had the full rear powerflex upgrade now for over ten years. Still in perfect condition, the improvement in ride and handling is well worth it.
I accept though the rose joints for the springpans may be the best way forward. However, since powerflex revised the settings on their powerflex bushes for the springpans, I would highly recommned you go this route, and don't pay the silly prices being asked for the rose jointed bushes. It isn't worth it.
For your information, the revisions to the latest powerflex spring pan bushes are:
1) The sleeves have been made a little more slim, so that fitting with the washer is now possible, whereas before it was a real struggle.
2) The inner springpan bush has been revised to the black series, rahter than the purple series. This makes it more resilient, which is probably a good idea as it stands 'alone', compared to the bush at the other end.
Some will say that the pwerflex bushes 'kill' or reduce the passive rear steering effect on these Alfas. From my perspective, I haven't experienced this at all. But I'm sure there will be others who say it does.