I have owned several.. and I still own one.
Yes, the spider uses reciprocating ball steering, but even then, many magazines wondered how Fiat got such good feel out of that box. It is not Rack and pinion tight, but it feels better than a MB roadster.
Fiat 124 transmissions -are- made of glass. Unlike many cars, they use springs to hold the car in gear instead of springs to push it out. Shift it gently and it's ratios will amaze. I always loved the third gear run out to 7 grand..
The small 9 inch solid discs front and rear will easily lock the wheels. It may lack in ultimate finesse, but does a decent job. The handbrake on the other hand, is about useless. NEVER trust it to hold the car on even the slightest incline.
The charging system is marginal. It can power everything the car comes with from the factory, but do not think of adding lights, powerful sound systems, or the like without uprating the alternator.. they also like to cook their batteries (which are in the trunk)
I always found the convertible top to be one of the easiest to operate and seals well. You need to make sure that the wires that hold the sides down over the winds are tight and that the drain tubes are functional. I would also make sure to extend them to under the car. From the factory they drained into the sills..
Which leads to...
RUST
Fiats Rust.. it is a fact. Most of it comes from the soviet steel they got in payment for a factory they build for the Russians to produce the Lada. It was never "cooked" at a high enough temperature to boil off the contaminants, so it had rust built right into the car.
Combine that with Fiat not understanding weather outside of Italy, shipping cars on the decks of ships, and dealers who never bothered to wash off the salt before undercoating, and it is amazing that any 124s survive to this day.
Overall I found them to be a very fun car to drive. They are nose heavy tend to plow when pushed hard in stock form. They are also under tyred from the factory Tjarrda, who designed the spider, once remarked that he designed the car with wider rims and tyres, but it came from the factory with the same wheels as the standard 124 coupe' and Sedan.
Hop up parts are out there. If I were to build an engine today, I would raise the compression to 9 to 1 (from it's 7.5 or 8 to 1, add some cams, Bolt on the later injected spider's intake and Microsquirt it. There are also exhaust manifolds and systems out there too. I would expect about 130hp.. which is plenty for such a lightweight car