I have both a 2.0 veloce 156 petrol for 7 years has been the best car i ever had and i now have replaced her with a deisel 159 1.9jtdm s-wagon for these reasons:
1. newer more reliabilty (hopefully)
2.Family Safety the 159 is fantastic i watched the crash tests for the 159 on youtube, i was amazed!!
3.More room, wider car and a little bit more room in the rear seats.
4. Well look at it!! the 156 is still handsome but those lights and gill on the 159 its EVIL!!
5.Fuel is going to be a bigger problem and i keep my cars for years so all though i thought i would never say this
deisel is the way to go even if it does feel wrong on an Alfa.
6. best of all i have gone for the sport wagon its is even prettier(IMHO) than the saloon has rear
washwipe and seat that fold down unlike the saloon which has fixed seats (Ti excluded),
Means when i go to Ikea i dont look like a total prat as i do with that small booy opening.
Could go on all day mate but i think you just want us to convince your wife
and i have to say in the case of the 159 i completly understand.
Go for it if you can afford it.