Increasing the level of the torso adds yes Hit Points every level you reach in torsos adds +5 HP, the maximum level is 16, at this level you get a increase of +75 HP on your torso.
Example:
Thats a Level 11 ultraspade(TORSO):
None of mythical items have any super power, and you can also add the damage their weapons and their drones, weapons at the maximum(16) level gain an increase of +15 damage and drones at the maximum level(6) gain up +5 damage (as grapling hooks, charges and teleports).
More examples:
Level 11 Needle Blaster Mark II (WEAPON):
Level 5 Triple Laser Pointer(DRONE):