Chilli Monster is 100% correct regarding road access.
Silverstone used to be a nightmare, however since the building of the A43 they use it as a dedicated dual carriageway to the track, there is no through access on this road during GP weekends. Unless Donnington has a similar plan I fear total chaos.
I can see a situation where someone may take a 2 hour flight to watch the GP only to be met with an even longer journey (time wise) to get from EMA to the track!
In principle the GP is good for the airport and the area as a whole, however unless the access is sorted out first the whole scheme could easily turn into a disaster for those it should be benefiting.