Probably easier to get from Lewes to Brighton pre-match on the shuttle trains than from the racecourse though, and quicker to head North after from Lewes too.....
Three car parks in North Street usually the best bet......go right to the bottom of the street if the first couple are full, almost always spaces down there.
Not a bad idea.....driving in and out much easier, and parking much cheaper. Most of the car parks in Lewes are £2-4, the one at the station is a bit more. Trains not usually a problem on a Saturday.