ouch!! As you said lucky it was a wall and not another car or worse a person.
Atleast its only easy to replace parts albeit costly. More of an inconvienence than anything and something you could do without.
Same thing happened to me with the wifes Metro Gti several years ago. Nothing parks outside our house 364 days of the year, but the day the handbrake fails a lorry happens to park up on the grass. The car went backwards down the drive, through the gates across the road and hit the back end of the lorry.