My comment about "successful" is related to their being an excessively modified form of a previously good design. The original carbureted 105's were quite reliable, light, quick, and comfortable. The 1750 was still a pure evolution, and I was always happy with the reliability and performance of the Spica. They were still reasonably light, and uncluttered designs. Then things started to be done in response to rapidly changing safety and emission regulations. Ride height, bumper mass/ugliness, cushier and heavier interiors. They became an amalgamation of compromises, losing the purity and elegance of their original design.
Other cars from that period suffered similar fates. Alfa did what they could within restricted financing. I enjoyed owning an S3 Quad for a while, but they were the blunted end of a once-sharp stick. The S4 was at least an honest effort to embrace the "touring" nature that the car had become, shedding the add-on engineering, cleaning it up, and accepting that comfort was now more important than quickness.
If someone would like to have a fun, open, sporty car for small money (comparatively speaking), a well sorted S3 is a good choice today. Still, they are not "great" cars compared to many others made by Alfa, and others. If I'm betting my cash on long term appreciation, I prefer a best-in-class design, made in very limited numbers. These two elements are always a good guide for investing in anything... Art, coins, cars, airplanes, houses, etc.