I've just banged off a Technical Support query directly to Pierburg in Germany. If/when I get a response I'll put the details up here.
I've had a very quick and informative reply from Pierburg.
The points to note are:
1) Pierburg part 7.00063.10.0 is the LATEST part for the After Market and is the same part for Fiat, Lancia, Alfa Romeo, Saab, Opel and Vauxhall have as their OE-Version.
2) From the list of previous Fiat part numbers I supplied it was confirmed that they are old versions of the valve but information on what design changes were made were not available to my contact.
3) Pierburg have had no problems with the solenoid, the valves, the springs or anything else.
4) Problems people are having is due to pollution of the valve and this is down to ECU maps and not the EGR valve iteself
5) They have had no After-Market valves returned under warranty since its availabiity in the After-Market program.
From the above response my EGR strategy will be as follows:
a) Buy a new Pierburg 7.00063.10.0 valve from the cheapest source I can find.
b) Fit the Fiat bullet restrictor plate, obviously introduced to reduce pollution of the valve
c) Fully dismantle and clean the old valve, polish sliding parts etc. and put in the boot of the car with the spare wheel as a backup part for on road events.
To me it seems there is no point is messing with back level valves. Bite the bullet get the new latest valve, fit and hopefully forget.