CMedina,
AA already has competition in New York from Aeromar, Continental and USAirways, all with regular scheduled service. For the real cheapos, there's also North American Airlines' scheduled charters. If those 5 airlines going head-to-head doesn't lower fares, I don't know what will.
Pan Am's POSSIBLE flights from Puerto Rico, Sanford and, pardon my laughter, Bangor, will do nothing to lower AA's fares. Pan Am does not serve the New York market. Pan Am's fares are never particularly low. And Pan Am's oddball scheduled frequency (e.g. Tuesdays and Fridays only) means that they wouldn't provide any competition anyway.
Most importantly, though, is that Pan Am, if they ever actually start any of these announced destinations, will stop them soon thereafter. And everyone knows this. Pan Am's impact is less than nada.
So don't "welcome Pan Am" unless you enjoy causing displeasure to the poor suckers who will try to fly that porqueria enterprise - it will do nothing to lower YOUR fares.