[major edits] Even if our consciousness is an illusion (even in the sense Denett suggests), the mere fact we see some information flowing across the universe means there is at least something that creates the illusion. That something is real - even though it might be only as real as a hallucintion (it exists). And if we can make our thought constructs, we can work with this information that makes what we are.
The obvious problem here is that if we think about our minds being simulated, we cannot see into the logic of the "real" world (world outside the Matrix). That's because in our world, we know that we can simulate only logical things (nothing illogical exists=is real) but we cannot know this is right from the "real" world.
But clearly the mere fact that we can think about this concept of the "real" world means something in our logic system.
So let's assume the logic we know indeed governs this universe. From this fact we know that our thought constructs (what we think consciousness is) are real (/hallucination-real).
And if our thought constructs are real, than cogito ergo sum is real - our simple logic "if something exists, than it exists" (Hilbertian axiom a→a).
Doesn't it prove that if our logic system is true, than we exist?
I understand this might be an awfully broad question, so I'll be grateful for any references.