Short answer - No, fitting a performance filter will not make any appreciable difference (definitely not at the power levels that Puntos put out). You will gain about 1 BHP or so compared to the old, dirty filter - but that same gain will be had by just putting in a clean, standard replacement element.
People who say things like "yeah, gives me an extra 10 horses..." etc are lying. A lot of people will "think" the car is going faster, just cos they've hyped themselves up so much.
As for induction kits, in a lot of cases, you can actually lose power, and especially low down torque. Occasionally you may gain about 1% right up in the rev range, but only if you've got a proper cold air feed setup (and not too cold, as the fuel won't suspend properly in the air).
You've also got other effects such as reflected shockwaves etc in the airboxes. Getting rid of the airbox will disturb this. In almost all cases, these effects don't contribute much, so you won't notice a difference. In a tiny fraction, you may gain an unnoticeable amount, likewise, some will lose out.
There are benefits to the high performance panel filters though - I must confess, I've put one in my girlfriend's Punto. That was because I managed to get hold of it for the same price as a standard element, and it can just be cleaned every year or two, rather than having to buy another one.
Oh, and by the way, I'm doing an engineering degree, and we do flow work as part of it. I can tell you that the flow a small engine as what is fitted to these cars will never draw enough air to be anywhere near the limit to what the filter can provide - changing the type of filter makes very little difference at these flow speeds.
Sorry to ramble on, but I get fed up of people who reckon their car's "sorted" because they've slapped the first "induction kit" on they could find. They'd get better results by cleaning all the carbon deposits out of the induction system, and setting up the mixtures etc properly. For power gains, you want to sort out the rough edges and sharp bends elsewhere in the induction system before fitting an expensive filter.
Other than that, if you can get them cheap, they are worth it just for the fact you don't need to keep shelling out to replace them every year - just clean them
and the sound was :yum: i prefer it to induction kit sound 
