We need to take in account another key factor, the price of the coins, and no one knows what will happen in the future, maybe you mine, you hold the mined coins and these coins will have a value of 5x or 300x in one year from now o maybe the value will be something close to zero, who knows.
I like what you wrote and especially this point which I think sums up what I am doing. Mine stuff that I think are good and could have a future and then mine some others and see what happens. I think the ROI point holds true and if you really don't care if you get the money back (me) everything is a win win or if it goes to 0 then it was a fun experience but the future does not look good. When I want to buy something, I always bring up ROI with the wife and I can usually talk her into buying it. lol