There seems to have been Engine mods at the introduction of the Sportwagon, have a look at '156 2.0 TS engines, which is which?' topic in general discussions.
Apart from that I don't think there were any changes, maybe the inclusion of side airbags?
The big changes are being made this year with the introduction of the 2.0 JTS engine and the new interior.
Better to look at general condition and options the car has than if it was made in '99 or '00.
I've tried both V6 and 2.0 TS and although I love the sound the V6 makes, I really think Alfa should have dropped it's 3.0 in the 156, the 2.5 lacks torque IMO. The 2.0 also feels lighter somehow, maybe it's down to the added 70kg over the front wheels of the v6.
So you've written off your 2L? The only differences I saw in 2000 year's model as to '99 were airbag also on the passenger side and leather steering wheel. I'd say you should look for the newest with lowest mileage.
Nice day today. Would love to out on the open road instead of sitting in Annankatu!
The newest with the lowest milage is my idea too. There is a very tempting white V6 with 45tkm at Hertz. White is not my first choice though. I would prefer a metallic or black. My search starts today...