the southern cassowary is the biggest of the cassowaries and i think you'd be hard pressed to argue that it is any less attractive than the other two species. i think the only reason you find it "less interesting" is because it is more common that the other two. i'm not having a dig - i agree establishing all species in captivity should be a priority - but i think when it comes to comparing the three, its pretty unfair to rate them - all three are equally splendid animals.
Yes, the Southern Cassowary is surely just as attractive as the two other species, no doubt about that.
And you are absolutely right that I found it less interesting as it is the most common species in captivity, it has been breed very succesfully in many insitutions and is a common species in zoo collections worldwide. The Southern Cassowary is also relatively well studied in the wild.
But very little, almost nothing is known about either Dwarf or Northern Cassowary, to be honest I know of no recent studies undertaken on Northern Cassowary in recent years, in the wild or captivity. Very little is also known about captivity husbandary, and aim sure we would gain much knowledge if anyone cared to bring back these species into captivity.