Thanks for the input!  I'll keep shopping around, but glad to hear that the roof spoiler hopefully shouldn't snap off.  

I understand your concern... but, the rear roof spoiler on the MINI is mounted very solidly - you can test this by pushing down on it.

The other fact is the way the rack is supported on the rear.  There are 2 straps on the top and one each on the sides (in addition to the two bottom straps).  The top straps share the load with the side straps.  The way the rack is cantilevered with the weight of the bikes on the rack, the top straps only share 'some' of the load.  Unless you mount two 'heavy' full suspension mountain bikes, there should be no issues.

I am researching trunk/hatch-mounted bike racks for my 2015 F56.  No factory-installed roof rails, so that rules out a roof rack for now.  The Yakima trunk racks look promising (Fullback 2, for example), but a bike shop guy expressed concern about the roof spoiler being vulnerable to the straps and the weight of the bike(s).  It's a solid spoiler; not the pass-through spoiler on the R-series. 

I realize there will be some wear and tear with trunk-mounted racks, but has anybody had issues with the spoiler?