I've not driven a 156 for a long time, so can't really remember what the 2.4 was like in it... However having owned a Brera and Spider both in 2.4 format, I can say it's a peach of an engine with a fantastic 3rd gear pull!
That 5 pot really has the edge over the 4 pot 1.9 and sounds reasonably good when pushed hard. The 210bhp variant is good for 270+bhp and 425+lbft of torque with a simple tuning box or remap for not much money, and that totally transforms the performance, making a good arguement against the 3.2!
Real world fuel consumption with mixed driving should be around 34-36mpg...
In terms of problems these have been well documented in this lounge... but to summarise consist of the usual EGR clogging issues which tend to be more common in low mileage users, and DPF regen issues with similar driving habits. EGR and DPF can be deleted of course, or theres the modified gasket for the EGR... Water pumps can fail occasionally as the impellar is plastic and can shear off, although replacements are metal!
Front tyre wear you need to be aware of, if the car hasn't been set up properly in the geometry department, the odd steering rack failing isn't unheard of, windscreen creaks, and wind noise aren't uncommon either... There are other small issues, as I'm sure others will tell you, but in reality they are well built and screwed together.
All of the above are easily fixable, if they haven't been already and the 159 is a great place to be! I now have a ti although in a 1.9 that's slightly tweaked and love it to pieces!
If money had allowed though i'd have not had a second thought about buying another 2.4!