Not sure if you mean one of the original Alfa spiders, (like in "The Graduate",) or a GTV spider. The former is a classic bit of kit, lots of class but not really an every day car. The later ones had a ghastly body kit fitted that ruined the simple clean looks.
The GTV is a beautiful car, but sadly its an old school Alfa, cramped and not very well built, (exept at the very end) and the spider is, as Jay sayes, prone to a lot of flex in the chassis. The lovely 3.0ltV6 engine is a joy to use, and even to look at! The boot space is a bad joke, and the rear seats are virtually unusable. 6.5 0-60 is pretty respectable, but they are also pretty thirsty, plus group 19 insurance on the V6 will be expensive.