Let's get the obvious out of the way. Yes, they're both mid-engined and made by a company owned by an international automotive empire. But the similarities run much deeper than that.
-Both utilize advanced frame construction never before used in a similarly priced car.
-Both share an engine from a humble entry level car
-Both have manual steering
-Both make extensive use of sheet-moulding composite body panels.
-Both are of similarly limited usability in the real world.
But clearly, the Fiero is seen as a bit of an odd joke whereas the 4C is seen as one of the purest sports cars on sale today. So what went wrong with the former? Well, several things. The first elephant in the room is the reputation for engine fires. Certain 1984 model year Fieros had issues with oil getting into contact with the exhaust manifold, and burning the whole car up. The issue there was an improper dipstick. You see, the dipstick said the oil capacity was only 3 quarts (2.84 litres) whereas the actual oil capacity is 4.5 quarts (4.26 litres). Due to engines running low on oil, there was increased stress on connecting rods which could suddenly cause all the internal combustion to become external. Happily, there has been a revised dipstick fitted to most 4 cylinder cars to prevent this from happening.
The next issue is the overall performance. 4 cylinder models were slow and unwilling to rev, so a V6 car is really where it's at. Then there's the fact that it felt a bit cobbled together. The suspension didn't really feel that buttoned down, and grip levels weren't that great. The latter can be easily fixed with fitting of some modern high-performance tires, and a company called The Fiero Store offers two stages of suspension packages with various damping options ranging from $329.95 USD for the cheapest stage 1 package, to $1250 USD for the Koni-equipped stage 2 package.
Finally, the big issue that makes some people shy away is the image. Many see the Fiero as another embarrassment in the history of General Motors. However, if you look past the haters, you will realize that you can get a good condition V6 car for $2000-$3000. A small investment in the form of the handling package (the $799.95 KYB-equipped stage 2 package appears quite good), modern tires on modern wheels (figure about a grand for brand new Direzza ZII Star Specs on tasteful new 16" wheels), and whatever little restoration bits your car needs (seat skins, minor trim bits) and you could have a very well sorted, fun to drive mid-engined car in great shape for under $5000 US. Sure, that sounds like a lot of money compared to an AW11 MR2, but it won't rust like the AW11s do. Bargain 4C? You be the judge.