As written, this Gimmicks can be somewhat confusing to players and game masters alike. Some liken it to a prerequisite to possessing weird powers, others view it as being an augmentor to existing weird powers. The latter is the correct assumption.

Superhuman is intended to, "kick it up a notch" as it were, with regards to a characters weird powers, allowing them to perform stunts that would othwerwise be deemed "impossible" for any mortal man. Let us take the Gimmick "Monstrous Strength" as an example. As written, it confers a level of brute, physical power to a character, enhancing any sort of physical Task where brute force is a benefit, a human being with Monstrous Strength would be the equivalent of the Golden Age Captain America, Doc Savage or Hourman; a powerhouse to be reckoned with, but not over-the-top.

Add Superhuman to a character with Monstrous Strength and you get far more impressive results; imagine Doc Saavge stopping a train with his bare hands, Captain America leaping a tall building in a single bound, Hourman bringing down a building with a single wrecking-ball punch.
Suddenly your Pulp Hero looks a bit more "Super", doesn't he?
To make it a bit easier on gamemasters; use the assumption with Superhuman that if there is a Task that would ordinarily be deemed "Impossible", the Superhuman character has a better than even chance of performing it. While Doc Savage would have to rely on his ingenuity to get through that titanium steel door, perhaps the mild-mannered, bookish fellow with the rippling thews might give it a go.
Somebody hold his glasses for him, this is going to get loud.