156's are great drivers cars, and depreciate like no other, apart from big French barges perhaps.
A good one will be a fine buy, and a bad one the worst buy imaginable.
Weed them out an find a minter. 1.6 doesn't go well enough, and will have been thrashed most likely.
1.8 and 2.0 are fine engines.
I'd buy one if it had:
1/. FSH by an Alfa dealer.
2/. Very low mileage.
3/. Silver or red paint.
4/. A "D" reg.
5/. Was 100% spotless. No dents, scratches, stone chips, and intact engine undertray (most get broken on lowered Sport models). Unkerbed alloys.
6/. Had leather and air (they all have ABS).
7/. 1 non smoking owner.
The thing is there are plenty of these cars around, so you can afford to be very choosy.
The Sportwagon's are nice too.
Happy hunting.