The reason Alfa's are cheap secondhand is down to the terrible deprecation they endure in this country, this is probably due to their reputation as being unreliable and troublesome.
I'm now on Alfa number 10, the last three were 166's and before them a 164, all using the 2.0 Twin spark engine, none of them ever failed to start, none of them ever broke down, I've never replaced a clutch, exhaust, shock all the things you'd expect. Things have gone wrong over the years but nothing that would suggest there were troublesome cars.
A lot of the problems suffered with Alfa's has been down to lack of maintenance, but this could be true with any other car.
I have a Citroen Dispatch Van, two years old, it has 37,000km up on the clock, it had a new gearbox at 19000km, front bushings are now gone, fuel pump, immobiliser a lot of problems for a two year old van.
It might be true to say an Alfa that has been poorly maintained may be more troublesome than another manufacturers car, problem is if the timing belts aren't looked after and they fail the damage to the engine is severe and expensive to put right..
point is try and find one with a service history, and if you can find someone who has experience with Alfas to come along with you all the better.
If you want to run with the crowd, buy a Toyota, there's no better expression of individuality than owning an Alfa (best kept secret in the motoring world)