For me, I'd get an Elise or VX220 too. Nothing comes close, and although the straight line figures will tell you one story I can promise you that even a basic Elise will be easy as quick as a 350Z, if not quicker. It'll be a damn sight more involving too.
Other than that I'd be looking at an S2K, or a decent Impreza STi. The latter is far more fun than you think, and if you get one in the right spec it feels special enough to be a weekend car. Put it this way, we've got a hoon planned for October and I'm taking our Scoob instead of the BMW.
I'd also give serious consideration to a Boxster, get one at £7K and pocket the rest in case you need to sort the engine. More usable than the Elise, more special than a 350Z, and a flat six engine howling is a thing of great joy.