I have a 2008 Ti sportwagon (1.9jtdm) so hopefully can help you a little.
Mines covered ~70000 miles and has had the following work completed so far:
62000 - new gearbox, clutch & DMF - i suspect this to be a premature failure due to the car being used for towing by its previous owner?
65000 - new cooling fan ECU
68000 - new EGR valve & inlet manifold - fitted to try and cure a misfire / poor mpg issue
The handbook states 90000 miles for a cambelt but general feeling is to have it replaced early (between 60 - 70000 miles) - mine will be done when it has its 72000 mile service to be on the safe side. Cost wise budget for anything between £400 - £600 (independent prices)
depending on who / where does it
Colours - mines carbon black and has a fair few stone chips but looks lovely when cleaned up - the Alfa red seems to damage easily so much of a muchness IMO
The EGR / DPF system on these seem to produce the most issues tbh, the DPF can become clogged up which can be avoided by giving the car a regular 'italian tune up' or manually regenerated via software called FiatECUScan. I use a product called BG244 regularly as I only use supermarket diesel and is excellent for keeping the fuel system clean (it fixed my misfire / hesitation issue which the EGR/manifold replacement was supposed to) BG244
mpg wise mine is used for short journeys with the occasional longer blast and the average is 33 most seem to get more than this although I believe the 2.4 is generally around mid thirties as GCDBONES mentions - these & the 2.4 seem to respond very well to a remap coupled with an EGR & DPF disable - favoured tuners on here are AHM AHM
& Alfatune Alfatune
although cheaper alternatives are available e.g. Angel Tuning
Cost wise, mine cost me £13k in December 2010 but that was from Veloces which tend to be a little overpriced
Steering racks seem to be a common problem on these - search the forum and you will see what I mean
Other than that IMO still the best looking saloon / estate on the market bar none - good luck on your quest!