The photo in my avatar was taken when the route used to go over the gobblestones at the Tower & the photographer took the effort to get the back drop correct & you can instantly tell it was taken in London, i think the company was called Action Photo but the photo's i've had back from Marathon Photo's have been completely useless with mainly a backdrop of trees & little effort in capturing the event just taking a load of photo's for the sake of it & charging extortianate prices.
I've ran Paris twice & would definately reccomend it.Comparing it to Brighton i would have to go with Paris, both are very good marathons but the run around the Power Station in Brighton is probably the most drab area i've ever run around.
I can't see how it's the runners responsibility to know the route, what are we expected to do carry a map & compass? Does sound like a complete mess though but in truth i can't see how they can have a winner when runners had run different distances & i doubt if 38 mins would be fast enough to win a 10k.
I've been in a similiar situation in the past & i timed it that i did a long run on the eve of going & when i came home did another of the long runs, did'nt make a blind bit of difference to my marathon performance. Just enjoy the festival, you'll be fine.