The investment is relevant only insofar as it renders an assault on a PoW-coin unprofitable, for the defense from an attack is what keeps the coin from being valued less for its having suffered some manner of compromise therefor.
I'm trying to determine what makes a non-trivial investment, non-trivial. You are arguing why a non-trivial investment holds value for a crypto currency. What it does versus what makes it do. I'm going to write some poems . I could have written a sestina with the time I've wasted on you.
This is a paradoxical argument which derives from the impossibility of answering the question "How many hairs does a man have to grow before he has a beard?" Since there is no specific number at which an unsightly clump of hairs becomes a beard, the argument is that no useful distinction can be made between a clean-shaven man and Santa Claus.
A "non-trivial investment" in a PoW-coin mining operation is
definitively such when it consistently renders unprofitable the execution of an assault on the coin therewith.