I also got my tickets for late May, 2005.
I have seen the show in London a number of times - and, while disappointed that Michael Ball is not reprising the Caractacus role, I am fond of the production and would like to refresh my memories.
If it is almost identical to the London staging ( which was done at one of London's largest theatres - about 2200 seats or so), I suggest not to get seats in the very front rows. I think the 6th to 12th rows are probably best in being close enough to the stage to see the actors clearly while appreciating the magic of CHITTY soaring into the skies
For the sheer spectacle of seeing the CHITTY magic, I guess Dress Circle and Balcony will work as well.