When is more power not needed?

[eclimax13]

over the last few weeks ive been throwing the idea around of adding more power to my ht system...right now im running 200wpc at 4 ohms which for the most part the speakers are rated for....but im constantly suggested to throw more watts at the lsi's by the polk forums, yet polk themselves have told me there will be no difference other than volume which i have plenty...
so now we have the emotiva sale which is tempting me for the xpa5 which will deliver 300wpc...so basically when is more power wasted money?
also if i were to do this i would move the rotel down to the living room and give my energy's 125 wpc which have an efficiency of 93db...at this sensitivity would i even notice the added amplification?
when i upgrade i like to get a 2 for 1...meaning when i upgrade my home theater room i move the old piece to the living room and that gets an upgrade