Sorry to hear about the 4-Series. That's a nice spec on the MINI. I've seen pics of the wreath on cars before and never understood or asked, how exactly does the blessing ritual work? I'm always willing to learn
Ok so firstly, that is not a 'wreath' but it is a 'garland'
If you search it you would see it is widely used in and across many of our Hindu traditional ceremonies and prayers, not only for the vehicle prayer. The garland carries significance in celebration and blessing of purity upon where or what it lies on.
When we pray for our cars, we say that "we give it life" or rather we welcome the car as part of the family household and ask that this vehicle is protected and protects its occupants by as much as the spiritual world can shed protection over us. The garland is to celebrate the new comer and welcome them to the family and annointing of the vehicle. Many people will have differeing or slightly different reasons why the garland is out there and how they perform their car prayers across our different hindu religion but the main reasons are above (on a high level).
There are some articles with more info on this on the net, much longer reads so if you got a few minutes to spare then check it out. Link for one of them below that I found: