Personally, I think anyone spending £350 for an hour wants their head examined, no matter who the girl in question may be. How would you feel if the punt was shit? Even if its not, its unlikely to meet with your expectations (you know what they say about meeting your heroes- that youll be invariably disappointed).
The only girl Id consider spending more than £200 an hour on would be MissKDD, and that is only due to the reviews on here.
Ultimately its a decision only you can make- its your money. Spend it as you please.