I have just purchased an 80000 mile 159 1.9 with a very comprehensive service history that shows every tyre change as well as service. This may give some help as to what tyre wear to expect on a 17" model. The car was on a fleet contract so tyres would be replaced at 2mm:
Original Equipment tyre brand unknown
Front tyres replaced at 17972 miles with Michelin
Rear tyres replaced at 21832 miles with Pirelli
All four tyres replaced at 39097 with Pirelli
Wheel alignment at 39097 at two different locations, suggesting there may have been an issue with the last set.
All four tyres replaced at 66236 with Continental.
These Contis have now done 14000 miles and have 2.5mm front and 4mm rear. I will be replacing these early as I work for Goodyear/Dunlop and I really shouldn't use Contis.
Last year we launched the Dunlop Sport Maxx TT Dunlop – SP Sport Maxx TT – Precision powered by Kevlar
and actually chose the 159 as the car to demonstrate this tyre to the press at the launch. This tyre has Kevlar sidewall inserts and we wanted a heavy front wheel drive car to demonstrate the difference in steering response between this and a conventional tyre.
This is the tyre I'll be fitting to mine next. For high mileage drivers, I'd also recommend waiting for the Goodyear Efficient Grip which is launched next month. It is the first tyre to not sacrifice wet grip in search of low rolling resistance. It will suit those on the mpg-chasing forum, wheras the Dunlop (which is also specified by AutoDelta on their 159 Supercharged) will suit those wanting Alfa-esque steering.
If I can coax my car to 140,000 miles I'll give a longevity report on both!
I hope my data helps.