Not all organisms have a brain and for those with brains, the level of awareness or consciousness varies broadly, right?
No.
I believe "consciousness" is largely a matter of on or off. Obviously types of consciousness vary considerably and a gnat is not going to have the breadth and depth of conscious as a whale. A single celled slime mold has much of its "brain" external to its body. It knows very very little and is capable of learning very little more. More complex organisms have very little limitation but they can still only operate within the confines of the way they think which is strictly logical. To understand abstractions would require more capacity than most animals possess and it would have to occur within their language of which we are incapable at this time.
Part of the problem with communicating these ideas is that you believe in "intelligence" and I do not. I don't believe a condition exists in any life form that we call "intelligence". I believe all intelligence is actually an event and I call it "cleverness" for lack of a better word. In a nutshell there is precious little difference in the cleverness of a man and a porpoise. The difference is not intelligence, the difference is every porpoise must understand life and its world starting from square one. But a human has complex language with which he learns all the knowledge and wisdom of the last 4 to 40 thousand years. We start from square 150,000 where a dolphin starts from square one. Dolphins are little less intelligent but far less knowledgeable yet most people aren't even aware that it is language that sets us apart from all other life. Because of language we also start with superstition and illogic.
There must be "levels of awareness" since even an oak tree is conscious but it would be easy to overestimate the importance of such levels. An oak tree apparently needs little consciousness to thrive but still its nature is impossible to see from our perspective at this time. All we can do is speculate about what kind of behavior is adaptive for a tree and how the consciousness improves the odds of survival. There has been quite a bit of experimentation into these branches the last half century but still little is known.
Consciousness is primarily for survival but obviously it plays a significant role in reproduction and mate selection. Individuals avoid unhealthy, stupid, and dreary mates. Everyone wants a live one. Indeed, only the fastest most energetic sperm will fertilize most eggs. Even gametes are looking for a live one.