my '54 16v active sport has never let me down, when i first got the car (april '05) , i did have a few random warning lights, airbag, power steering, abs and handbrake, a trip to fiat sorted all that out and thankfully it was under warranty
i have read a few stories of juddery wipers, dodgy clutches and electrical gremlins, none of which i have experienced and hopefully never will - i am no granny driver either, so would expect a few to rear there ugly heads by now - *touches wood*
as for the realiabilty of the engine, if you keep it serviced and in good order, it will last