It's never a bad idea to add more power. The gains are more than simply increased SPL's. Music and movies will have more dynamics and the bass will be tighter, with better definition. Also, the entire frequency range should have a sense of effortlessness, without any straining in the sound.
I had added a Rotel 60watt/ch dual-mono amp to my old system after moving into my house. The increased room size coming from an apartment dictated more power. My NAD integrated amp, with 40w/ch, just did not have enough oomph anymore. I too was skeptical that only a 20w/ch increase would be enough. Let me tell you, my worries quickly disappeared as soon as I played music through it.
A dedicated amp will kill a similarly spec'd receiver.
Ed
* Sierra-2EX's W/V2 crossover upgrade
* (2) Rythmik F12's
* Parasound Halo P6
* Audio by Van Alstine DVA-M225 Monoblock Amps
* MiniDSP 2x4HD For Sub calibration
*World's Best Cables Canare 4S11 speaker cables