I have 20mm spacers on all four corners of my 2017 i3 BEV with 428 wheels (which I don't really love), and I think it looks great. Is there more stability due to the wider track? I don't know about that, but it seems good and smooth, even in the wind. And there's been no penalty in efficienty or handling, as far as I can tell. No rubbing.
I agree that pushing the tires outward a bit looks nice, especially if you have the skinny winter tires on the 427 rims. Spacers + black PlastiDip = a good looking combo.