Birdseye may or may not be a disease, nobody knows. If the leading scientists haven't figured what causes birdseye, then all we can do is guess. There are lots of credible theories & disease is only one.
Birdsye is usually pretty dense, and slow growing. Curly is usually pretty dense, too. From what I have seen personally, there's no standard of what maple is going to be dense. There's lots of variables to consider, from the growing conditions all the way up to how the lumber was dried. There's really no way to know without personally inspecting each individual piece. I will say that curly shaft wood seems almost to always be heavier than straight grain. But that goes back to the reason it's curly, which is related the density of the tree wrinkling & compressing under it's own weight.
