Well, I've never seen one Myself, so as far as I'm concerned, I'm not concerned. If I happen to see one, I'll be sure & pass it on.

I understand what you mean regarding matter etc. But of course films and stories can turn out to be wrong regarding the fact that they become twice the size. So lets say they change into one of about the same amount of matter. What then?
Of all the animals on Earth at present, the animal with the greatest brain/body mass ratio is the human being. The average human (150 pound body, 3 pound brain) has a ratio of approximately 1:.02 (for each pound of body mass there is .02 pounds of brain mass). The average dolphin has a ratio of about 1:.00825 (the blue whale mentioned above has a ratio of about 1:.000165). The two highest ratios in the animal kingdom are the human and the dolphin (by comparison, the wolf, a very intelligent canine, has a ratio of about 1:.00156).
Let us assume that the wolf requires its entire brain for housekeeping (a totally unfounded and, to me, absurd assumption). If this is the case, then the human brain has left over, after housekeeping, nearly 13 times the brain mass the wolf has that can be devoted to thinking.