The Aura's power strength bonus of 25% can only be increased with multiple instances of the aura. A single mod can only give a single instance of the buff. Two of it can give two instances of the buff, and so on.
Multiple instances of this Aura will increase the Ability Strength bonus only, not the buff duration.
Sentinel weapons with high status chance can easily proc Growing Power, thus removing the need to use specific Primary, Secondary or Melee Weapons.