After analyzing many lines and spending countless posts debating them in the Ponziani thread, I've come to the following conclusions:
1. Most of our time trying to develop sound theory for white is spent looking for ways to avoid black having comfortable equality. That's not a good sign.
2. The Fraser defense is a very serious issue for the Ponziani. Dave has come up with a few ideas, but they are best described as treading water instead of drowning. Not a good sign there either.
3. Black has many choices that can either be very complex or simplified into an equal position. In either case, I'm not seeing white create the kind of lasting pressure that I see in the open Sicilian or many lines of the Ruy Lopez for example.
4. The Ponziani would be a practical try for club players. Clearly if you put the time and effort into learning as much Ponziani theory as you can, you'll generally be better off in club-level games. Unfortunately, this is true of any reasonable opening.
So to conclude: The Ponziani isn't bad, it's just not very good.