I don't see any point paying £8k for another car that will be used for the same thing as you current car though - there's not much (if anything) an s2K can do that the Z cannot? For cruising around the Z looks better, maybe for the highlan twisties the s2K would be more of a hoot but not enough to justify £8k I wouldn't have thought!
I'd go for a s1 exige or elise - great fun in twisties, cheap on petrol etc - only drawback is you look like a tit getting in and out (I crawled out on my hands when visiting the lotus dealer lol)