Re: 156 buying advice
In my opinion all Alfas have high depreciation because of their reputation but you only buy Alfa for a reason - because you love em! :-)
I had a 156 1.8 Lusso which I bought for £2k with 60k on the clock and about 2 years later I couldnt get more than £750 so I dont think they ever hold their value. I was thinking for what was originally a £20k car, it cant really depreciate much more, but I was wrong!
The 2.4 models might be more difficult to sell on but as you can see from this forum there are plenty of enthusiasts so as long as its still in good condition I dont think you'll have a problem.
Look out for cambelt which have a tendency to fly off so recommended to replace every 36k or 3 years whichever first. Also look out for warn variator which makes the car sound like a diesel. Some recommend replacing these at the same time as the cambelt as you need to take it off to get at it. Upper front wishbones are often squeeky on the 156 but post 04 might have improved them. Look out for glowing tail lights even with ignition off caused by rev counter. I'm sure theres others but these are the real obvious ones. Service history is important of course, they tend to drink oil so watch out for that.
//The designer must unite creative functions with the technological ones - extemporize as a technician in order to dialogue with the technicians - in order to defend and assert the quality of his intuitions.// - Giorgetto Giugiaro