I've had my '77 for 2 years now and have put 8000 miles on it (it now has 62k). My advice, if you intend to drive yours daily, is to a) find a good Fiat mechanic (unless you already are one) and b) keep up on all maintenance, fixing the little things that come up as they come up. If you do this you will end up with a car that is, as I describe mine, "as dependable as my Lexus".
So far, I have had the head done (including port-matching), installed a 4-2-1 exhaust, had the brakes completely rebuilt, as well as the front end, and installed an electronic ignition setup. I also had the radiator re-cored and installed a new water pump myself. At the time of the head work, all of the engine seals, except the rear main, were replaced. Still to do includes rebuilding the rear end (it howls a bit at highway speeds) and the transmission (noisy input shaft bearing, but will probably include a clutch and throwout bearing).
The PO had purchased it after it had been sitting for a number of years, and had replaced the hoses and the original hose clamps, as well as the timing belt and other miscellaneous maintenance items prior to my purchase. Transmission and rear end have Red Line oil, but must've been driven at some point without adequate lubrication, hence the noises
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. Last fall my wife and I took it on a 1000 mile, 3-day tour with no trouble whatsoever. I wouldn't hesitate to drive it anywhere.
I look at it as a work in progress and consider the work that I've had done (and done myself) to be investments in the longevity of the car. Fiats are like any other car, if you take care of them they'll take care of you.
Good luck with your Spider.