IMO Alfas are a delicately balanced piece of electronically controlled machinery that is built with little resilience to wear or change, in other words they are built to be great when they are new >50k, after that all the major components start to fail as they do with any car and need replacing, the weak point with Alfas is that when you take something apart or replace a part it impacts on something else and gives other associated issues, which then knock on to other issues which is where the costly, continual issue syndrome comes from.
Alfas are seen as a sports car by many, so have generally had a life being pushed hard, this results in most second hand Alfas being a ticking wallet bomb, if you either buy one new and treat it correctly or are lucky enough to buy a well maintained and un-pimped / thrashed second hand one and carry out only required maintenance and drive it sympathetically you should have minimal issues.
From my experience with Alfas, if it ain't broke, you will probably break it when your fiddling with it.
All diesels have EGR / Clogging / Turbo issues, not just Alfas its the nature of the beast, all Manufactures have weak and strong points that's why there are so many different Marques on the roads, we all pick what suits our needs / desires, if you make a wrong choice, move on.
For what Alfas are, I love them, Would i drive to the other side of the earth in the 147 or 156 ? no , i'd go in my Saab 9-5 with 160k on the clock and get there in comfort!