> Sure, you could put a 3 Ghz CPU in your microwave oven or vacuum cleaner
To do what? Un-compress and display a video recipe from Youtube? Please be serious. I'm talking "Mega"/cheap and you answer "Giga"; you are off-topic.
Do you have any idea what is the cost of 1 MIPS in the low range nowadays? Answer: totally negligible compared to the rest of the SoC. And not just in dollars but in terms of power and real estate just as well.
Backtracking: yes, the extra performance cost of a micro-kernel would not make any difference to your microwave oven.