"As to whether this is different from sense perception - emphatically, yes, because it enables the intellect to 'grasp concepts' which are different from either perception or sensation."
Plato doesn't speak of concepts. But of the pattern or idea, think of the the case that in seeing a lion's tail, we see a part of the lion, leads Aristotle to say, when the tail is cut off, and no longer part of the lion, it is no longer part of the form, idea, or genus, lion, but it still has the
hyle.
You know, when we speak of taxonomic ranking, we need a big leap in order to say that humans don't really exist as a specific point in Evolution, that a tag like Homo Sapiens Sapiens is in some way just a "concept", rather than a physical fact about a manner of existing things intelligible under a peculiar faculty of the soul or life of the human being, the thinking animal.
I think the Thomistic sense you bring up has to do with syllogistic logic. I.e., with the intellect understood as the power to make inferences from established premises. The premises themselves bring us back towards the world. I.e., someone says, Crete is an Island. It simply is so, it takes a theory to say that a specific faculty of the mind establishes it logically as a judgment based in a psychology. That the judgment might be defective, as in the case of a mad person. And so forth. This all pastes a web of assumed thought over the discussion in Plato, which we ourselves have a hard time not superimposing through thousands of years of habit and breeding into this thinking according to a selection which Plato was not the product of.
"Intellect is to be distinguished from imagination"
Of course one does make that distinction. And yet for no clear reason, we perhaps simply "know" to. There is a second issue of the ineligibility. Because we know what a human being or a gigantic piece of granite is, in dream and memory, just as in the surrounding world. In this sense, it is hard to understand how one has a sensorium in dreams. One sees things, for instance, in a dream. In a dream, we are still in a whole, as it were, where all things distinguished are significant according to the whole, and belong together in it. Each is the same insofar as it is one of the things in the world or dream.
Why, then, is there not sight in a dream? Or, how then, is sight in the surrounding environment to be distinguished? What is the cardinal or demonstrably knowable difference?
It's interesting that, indeed, in machines that translate brain data into images, the same result is got from waking images as dreams so far as the reproduction is made. Such machines work by the correspondence of visual images to brain data, through building an encyclopedia of brain states correlated to images.