The way I interpreted the rear spoiler rule, the mirrors are not included. The rules state that the spoiler can not protrude beyond the overall perimeter bodywork of the vehicle as viewed from above. If directly below the spoiler is ground and not some part of the vehicle, then you went too far.
For the front splitter. AOA is free in SP, at some point it stops becoming a splitter and becomes a spoiler. As far as protrusions, I went as far as having endplates and had my flares extend to the splitter. I wouldn't blatantly add a canard to the splitter or anything horizontal that can be perceived as a wing. And according to the rules, anything you do has to be within the overall perimeter of the bumper as viewed from above.