I bought a 06 159 3.2 nearly 2 years ago now , and on the whole it has been very reliable, more so than the 4 previous 156's
So what's gone wrong. had to replace the power steering reservoir, and refilled with green fluid, rather than the thicker red. My Alfa had only 27K on the clock , check other threads about whether to replace fluid if yours is red
Needed to replace a coil (BTW : OEM coils from Alfa are hideously expensive.)
New Plugs : When they changed my plugs , the rear 3 plugs hadn't been changed for ages, as it seemingly requires more work.
New front brake pads - the old pins had to be drilled out
I change oil every 6K - hopefully to help avoid the stretched chain fairy from visiting
I also needed 4 new tyres , as the tracking was off - again see other posts (4 18 inch tyres weren't cheap) all badly worn inner edges , and on initial inspection looked OK
On this age I would also check for any subframe rust issues -mine are fine , but others have reported problems.
My paintwork is fantastic for it's age
Needed new front badge as original was badly faded.
Rear passenger footwell leaking water from door seal , yet to get sorted, seems reasonably common.
Around town I get 16/18 mph , shade over 30 on long runs and Tax is £500 / year.
She's a completely different drive to my previous 156's , and she is heavy so she is not a pocket rocket even with the 3.2 , but she is great to drive , and she eats up the miles with gusto, and mid range acceleration is good . The Q4 system is v reliable and works fantastically well, even in the snow (I,m up in Aberdeen).
Hope this helps, if you want any further info - just let me know