I had three Spiders. The first was a 2000-model phase-2 TS, ex-Japan, really tidy car in Zoe yellow. I always felt the performance was adequate but not outstanding. Not as good as a 156 - it felt heavier. In particular, I found it difficult to set off quickly from a standstill - seemed that first gear was too high. The rear shocks seemed too stiff in relation to the fronts, too (they were all original, it only had 80,000km).
The second Spider was a phase-1 TS from 1997. Pretty tatty all round (one-quarter the price of the newer car) and over 160,000km but a much more fun drive. The engine (with the alloy top) had a totally different character - seemed to have a lot more 'zing'. The EGR had been blanked. It was easier to set off from a standing start than the later engine. It was also more economical. I suppose there's always a slight bias with expectations - but even so, the earlier TS Spider worked really well.
My third Spider was a 2002 (late phase-2) V6. This was a smooth and powerful drive and the front/rear shocks (stiffer at the front than the TS) seemed nicely balanced. Contrary to what people say, I found the steering more accurate with the V6 in the phase 2 rather than the TS in the phase 2. Brakes were noticeably stronger too. Fuel economy was, as someone pointed out, hardly any different to the TS in practical terms. Around 30mpg for both of them on trips and remember that the fuel gauge lies at halfway and below (half really means a quarter of the tank remains).
My current V6 Gtv? It seems to drive better again than the V6 Spider - the ride comfort goes up another few notches, it's generally quieter, better headroom and visibility, and all this makes enjoying the performance far more satisfying. I think it's a great package.
So - my conclusion - If you're looking for a 'fun' car, go for a Spider and an early Twinspark engine. If you're looking for a 'nice' car, go for a Gtv, and a later V6.
But you really have to assess each individual car on its own merits - the above just gives you a bit of what to look for