Ghedi is much better base then Piacenza for traffic. Piacenza has not much activities even if you have nice photo opportunities from outside.
Ghedi is good only in the afternoon (sun on your back) so in winter time you have not much time to take pictures.
The spot squadmin indicated is correct but here you are very close to the fence and meteo station and they see you and it is very easy police comes out.
There is another spot just some 200 meters on the right of this place but to reach it you must turn right just after crossing the railway taking this small road. At the end of this road you must turn left end go towards the old military weapons station. Just passed trough you can park (pls pay attention where you park) and walk a little bit on your left. You'll see the base and also the spot near the fence from here but you are hided from base and it's safer.
Ghedi is a very strange base with local police... Sometimes you have not problem, sometimes they ask you to leave..
Remember to hide the scanner in Italy....
Here a photo I took some years ago in wintertime from this spot:
http://www.airliners.net/open.file/0809689/L/" onclick="window.open(this.href);return false;
hope this help
GP