What's special about the zodiac weapons?

Some chapters in Kid Icarus: Uprising have hidden rooms with special weapons in them, named after zodiac signs. For example, in chapter 2 you can find the Sagittarius Bow. These seem to be unique items; if you replay the level it's no longer in the room.

But at least as they are when you get them, they don't seem to be much better than the other weapons available.

Is there a way to improve them? Do they have other special abilities? Or should I be fusing them? If I do, is there a way to get another again later?

Solution 1:

Zodiac weapons...

• are required to get a gold laurel wreath on the level.
• unlock more weapon fusion options, though they still don't seem to be special in any way.
• unlock a square in the Treasure Hunt grid, required for finishing the Treasure Hunt and 100% completion.