Well steve - I have a Bell and Colvill 160 Sport S1 Elise - i spent a bit to it and sold it last year.
I really really loved that car and wish i didnt sell it - amazing accelation and awesome predicable handling (unlike my MR2 now which seems to step out when your not expecting it 2).
I can see you've had/got a Westfield and in my opinion they are very similar cars (same pick up and handling) but the lotus has loads of sex appeal and if you get a good price in the begining then in two years you will be able to sell it for the same money or £500 less max.
So what sort of money are you thinking of spending..... Personally the S1 is a better car due to weight etc so whatever you can afford i'd go up the S1 Range.
For £8-9k you can get a fairly good B&C or a VVC (Stay away from the 1.8i as the k-series engine doesnt do the car justice).