I have quite a few directories, the main directories a priced in GBP, I price about two directories in USD, the money those two bring I don't convert to GBP, they pay for adverts I buy from other directories and the GBP I draw into my bank.
I don't think pricing in GBP put people off if the pricing is sensible. I don't necessary have more inclusion in the one priced in USD than the one priced in GBP.