Here is a very simply way to look at the value and nature of consciousness.
1. In order to be successful an organisms actions need to be appropriate for the situation they find themselves in. Therefore there will be an evolutionary pressure towards appropriate behaviour.
2. Fixed and stereotyped behaviour can only be appropriate in an extremely stable environment. Exploitation of a less stable environmental niche will create an evolutionary pressure towards flexible behaviour that changes as situations change.
3. Learning from experience (as opposed to habituation, conditioning and genetic changes to reflexes and instincts) is a method that many animals use to maintain appropriate behaviour in a complex environment. In those animals there will be an evolutionary pressure towards more effective learning-from-experience.
4. Learning-from-experience seems to require:
a. a form of experience, some sort of outline model of reality.
b. a memory of past experience, snapshots of the model of reality categorized so that they can be retrieved as required.
c. a method for establishing cause and effect relationships between elements of experience, a cognitive process that establishes reliable causal theories.
d. a method for establishing the desirability of effects or outcomes, a process that gives goodness criteria or emotional colours to outcomes.
e. a way of simulating future experience and comparing it with outcomes, a predicting process using causal theories and a way to register the error between plans and outcomes so as to maximize desirability.
All these aspects of learning would be under evolutionary pressure to become more effective. In particular a powerful model of reality to be used to experience the present, remember the past and simulate the future is advantageous to this type of learning.
5. Consciousness is experience (or very close to it). It is the globally accessible surface of the model. It is not the thought processes involved in the formation of the model or in its use. The model is necessary for this type of learning, but it is just the model and not any sort of thought. However, when our own thoughts needed to be modeled, elements of the model will be standing in for actual thought processes.
6. The quality of the model (or consciousness) is going to be under environmental pressure to improve up to the point where its costs are as great as its benefits.
The picture lacks sophistication but until it fails me, it is the picture that I am tentatively trying to elaborate.