Having had recent experience of both cars, I can comment on the 156 v 159 debate as follows:-
My 156 was a 2.0 JTS Veloce in 130R with Alfatex interior and 17" upgrade wheels. Car was excellent. Totally reliable and great fun to drive. Very driver friendly, fun & quick. Ride was firm but not overly harsh. Engine was a peach. So much more tractable than a twinny but still just as rev happy. Even liked the brakes. Great on smooth roads and on the track but not so happy on a bumpy, twisty B road. Interior build just fine but ageing compared to newer cars. Overall, I'd give it 7 out of 10 and still miss it loads.
The 2.2 JTS 159 Ti is a different beast altogether. The rear is styled nicer than the 156. The rear arches are more pronounced. It's less tall, more lower, wider & squat. The perceived quality, particularly on the inside is a 100 times better than the 156 and a 1000 times better the the 320D M Sport loaner we had. Ride quality is excellent, even on the lowered springs & 19" wheels. It's a much more grown up car and a bit less fun as a result. The engine seems great but I've yet to give it full beans. It's not as easy to drive. Pulling off smoothly requires some concentration and the gear shift isn't as easy to use as the 156. The brakes are Brembo and are truly excellent.
Overall, better looking, built from better quality stuff, more comfortable, more practical (split fold seats but more cabin storage please), better ride & handling and better brakes & much safer (NCAP 5 Star). It is a big step forward and I honestly the best car in it's class. I'd give it 9 out of 10.
Downside is it's not as fun. You're less in touch with the driving.
Would I have swapped the 156 for it though if I wasn't forced to? Not yet I wouldn't. The 156 still had a couple of good years in it