I flew in to Naples couple of years ago, and I was overly impressed with the services available for spotting. When I went, there was a designated area inside the terminal for spotting, which was covered by shaded glass which was full of fingerprints - not so good for photographs! This facility was before passport control as I remeber it. But the registrations of many aircraft were visible, and a good view of the landing runway (usually 24) was obtained. Once you pass through Passport Control, there is a fairly good view of the apron, but it was dark and cloudy when I went, however in the right conditions it could be OK to get reg's I guess (when I went an Airtours A320 and an Air One 737-200 were parked right in front of the terminal). I was flying Air 2000, I was bussed out to the aircraft (G-OOOW) and on the way out there, Britannia's leased ANZ 767 (ZB-NBJ) was parked next to it, so I got that one as well. (as it happened, I was flying back to Manchester, and just after we touched down at Manchester, the Britannia 767 landed about 2 minutes after us, so it had been following us all the way!)
So, the terminal is a bit cramped, with few shops, but is good for the spotter.
Hope this helps!
PS. Have a great trip