My tuppence worth:
Cam belts, tensioners and water pump replacements every 3/4 years at around £950 not funny.
Recommended service interval is 72K miles or 5 years and an Alfa specialist (Autolusso prices used because they are easy to find on line) will charge £845 to carry out the replacement of the Cam belt, tensioner, 2 x idler pulleys, 2 x cam cover gaskets, 6 x spark plug gaskets, 6 x spark plugs and metal water pump. Autolusso recommend a 48K miles or 4 year interval. If you use top quality modern synthetic oil this service with a mid point oil change would cover most of the engine servicing for four years which isn't bad.
Suspension bushes wear quickly and need polymer ones
Most gtvs will have had the rear bushes done by now but if not, it is a once only job.
Expensive on fuel
I get 20+ mpg even when I give it welly. 28-29 if I take it easy cruising in 6th gear.
Expensive on road tax
£220/year pre-March 2001 £270/year for later 3.0 v6 models
Expensive on servicing
See earlier answer. So far (2 years) mine has cost me a set of front and rear pads and discs, a stainless exhaust, oil and air filter plus some oil and 2 x MAFs (previous owner had fitted an aftermarket filter which the MAF didn't like - reverting to OEM filter solved the problem). Service parts are all inexpensive. (From memory, less than £150 for four discs and two sets of pads)
Lambda sensor needs replacement at around 60k?
Not sure what this one is about (touch wood!) Lambda sensors seem to be a problem for most makes of car eventually as they get older.
Then there are the inevitable electrical mysteries.
My airbag light comes on if I forget to make sure that the ignition is off before moving the seats. Heated rear window needs to be re-wired to include a proper relay to protect the fuse board. Radio (aftermarket) needs to be disconnected properly to prevent the battery from going flat but this is mainly due to the original head unit having a proper off switch. When it comes to electrical problems, a gtv is not in the same league as a more modern CANBUS wired car!
"When you sit in a Focus RS or a Golf R32 itís like sitting in a commercial for Lynx aftershave. When you sit in an 147 GTA itís like sitting in a Venetianís hand-made suitcase." J.Clarkson 2003.
Current fleet: 156 Sportwagon jtd 16V (facelift) 2.4 Spider, Leon Cupra SC
Projects: Spider S4, Matra Murena 2.2