I've been parking at KES for years. Secure car park, pay as you go is £5 a game, but for the last few seasons I've had a season-long pass - this year it's £95 for all home league and cup games, together with a reserved/numbered space on the car park. Money goes to a good cause and the stroll across Aston Park past Aston Hall to the ground is in my view the best approach to a football ground bar none.
As for getting away after the game - if, like me, you stay right to the end of the game it can be a bit of a queue to get back to the main drag, especially if it's a big crowd. But if you leave before the game finishes, or if it's a lowish crowd (as it's likely to be this season), it's pretty quick to get away. The only problem this year is the M6 roadworks at Jct 6 until December - details on separate Tickets and Travel thread.