Can an observer-independent phenomenon, add meaning or value to the life of the observer? If no, then, assuming the physical world as observer independent (as in, it exists in a state without me observing it) (maybe because someone else can), and consciousness as the only subjective perception, is it not impossible to reduce consciousness to purely physical or biological terms? And also comment on the hypothesis that consciousness is the only thing that gives life its meaning/value.
Sure, consciousness is reducible to a subjective first-person ontology, however, we just don't have an adequate objective third-person epistemological account of how consciousness happens in the brain to say much more than neurobiological processes in the brain cause intentionality. See Searle, "The Problem of Consciousness" for a heuristic approach to an objective third-person epistemic explanation and accounting of first-person subjective ontology.
In Sealre's concepton even an imponderable utterance such as "you mean everything to me" is meaningful in that the utterer intentionalistically uttered the noises "you mean the world to me" and sincerely intended them to mean something akin to "you are very important to me." For another example, imagine you are in the Army and your commanding officer sends you to the top of a hill to scout the position and armament of the enemy force. You are told to wave your arms if the enemy is well fortified. When you get to the top of the hill and see that their battalion can easily overwhelm your squadron you satisfy the conditions of both utterance by waving your arms and the sincerity condition of waving your arms to indicate the message your commander has requested. If, however, you get to the top of the hill and there is no enemy but you are attacked by a swarm of bees causing you to wave your arms in self defense, the utterance is not intended as the meaning assigned, yet might be interpreted as such.
As for a "good riddance" to mind-body dualism, check out Professor John R. Searle's course lectures for Philosophy of Mind from UC Berkeley. They are available for free on iTunes and YouTube
That said, yes, the causal powers of the brain which achieve intentionality and consciousness are the cause of meaningfulness.
Can an observer-independent phenomenon, add meaning or value to the life of the observer?
Sure, if you find a mountain meaningful and knowing it exists adds value to your life, the yes but the observer-independent phenomenon didn't add the meaning, the observer did.
If no, then, assuming the physical world as observer independent (as in, it exists in a state without me observing it) (maybe because someone else can), and consciousness as the only subjective perception, is it not impossible to reduce consciousness to purely physical or biological terms?
What else could consciousness be? ;)
And also comment on the hypothesis that consciousness is the only thing that gives life its meaning/value.
Yes meaning and value are observer-relative and without conscious observers, there is nothing observer-relative.
Consider as well A.J. Ayer's thoughts "The Meaning of Life":
Evidently, there is no general answer to the question what constitutes a meaningful life. A life lived in one culture at a given social and economic level which satisfies one person might well fail to satisfy another who dwelt in a different or even in the same environment. Treating the question subjectively one can say, platitudinously, that it is a matter of the degree to which one achieves self fulfilment. Treating it objectively, it is a matter of one's standing in one's society and the historical influence, if any, that one exerts. We have seen that the results of these different viewpoints need not coincide either with each other or with what we humane and liberal persons would regard as morally commendable.
(also as posted in this answer you might appreciate)
Logic alone is enough to show that meaning depends on consciousness. If not, then one would have to be using an odd definition for 'meaning'. Meaning is in the eye of the conscious beholder.
Yes, it would be impossible to reduce consciousness to purely physical or biological terms. There are those who believe it can be done but no evidence they are right. Chalmers would say they are not thinking straight and I'd agree.
You ask about philosophers who 'get rid of' the mind-body distinction. Off the cuff I'd recommend, in chronological order, Nagarjuna, Kant and Francis Bradley. All philosophers in the Perennial tradition 'get rid' of this distinction and all others. They would be conceptual, not metaphysical. Hope this helps.