I feel for you. I had someone do the same to my last e46. I was visiting someone out of town, only to find a police notice on my windscreen the following morning, informing me of the damage. 10 cars on the street had their wing mirrors kicked off. My door and upper front wing were dented by the force. BMW painted nearly the whole side of the car (Titan silver paint - needs to be blended in over a large area to look right).
Check eBay.. there are loads of Z4s 'broken' for parts. Here's one: http://www.ebay.co.uk/itm/BMW-Z4-E85-E86-SI-SPORT-3-0-PETROL-CONVERTIBLE-2007-4X-WHEEL-NUTS-BREAKING-PARTS-/282419818842?hash=item41c188715a:g:Jt0AAOSwPcVVvORJ
Looks like the dent on the door can be repaired by a dent man.
Check eBay.. there are loads of Z4s 'broken' for parts. Here's one: http://www.ebay.co.uk/itm/BMW-Z4-E85-E86-SI-SPORT-3-0-PETROL-CONVERTIBLE-2007-4X-WHEEL-NUTS-BREAKING-PARTS-/282419818842?hash=item41c188715a:g:Jt0AAOSwPcVVvORJ
Looks like the dent on the door can be repaired by a dent man.