Bluemofia
F=ma
...and such lifeform will be very simple as all its energy and function will be totally devoted to surviving on low yield molecules, oxygen based lifeforms evolve into higher life forms because oxygen provides more energy then is needed to simply survive. Earth had billions of years for non-oxygen life to evolve and what happened, it stagnated, without the high energy oxygen system it hit an evolutionary wall.
Not necessarily. Evolution isn't anywhere near stagnant if you are on the borders of survival. Those that evolve fastest are those systems in high strain environments, because selection is strongest there. This is a very well supported concept, as pampered organisms do not evolve very quickly. Evolution isn't like energy points left over to be spent into evolving.
After oxygen came about, it pretty much nuked everything, causing microbes to either adapt to ignore it, use it, or die. It was a huge selection pressure to survive oxygen initially, not because it suddenly was a gift to allow complex metabolism. That came later after the survivors were competing for the edge amongst themselves.
PS on your food analogy, did you know that the current theory on our evolotion as humans states that the high energy yield of meat and our domestication of animals for food is the reason our current civilization happened. They found that all humans who did not take that route and survived on low energy vegetables or hunting alone never advanced, and you know why, because all thier time was spent on simply surviving, they had no free time to contemplate and advance thier society so it stagnated.
I wouldn't say domestication of animals for food, but rather a high enough degree of specialization in farming crops allowing the populace to specialize into non-food gathering jobs. (Aztecs did not have significant domestication of animals as far as I know, and yet they had a fairly vibrant civilization before the Spanish came)
Likewise, those that have domestic food animals don't always develop great civilizations, such as Egypt, whose rise to greatness started with abandoning large scale animal domestication with the desertification of Africa, and adopted a grain based agriculture.