Yes ,What i meant is , Overpowering too much can blow up speakers ,since wattage produce heats with magnets in the speakers.Mr James, i agree too much of power is bad. But, it's not too bad like powering the power hungry speakers with underpowered amps. With high power amplifier you have got two tools to save your speakers and your amplifiers. Volume knob and ears. It's in fact hard to kill a speaker or electronics by feeding too much power unless one badly wants to murder it. More power is always good.
Also underpowering can cause clipping which is very bad for speakers than overpowering speakers with safe volume levels.
Agree that every speaker have difference in tonal quality. But to get the best improvements you need to spend a lot with other speaker brands , and you need to go next high line /high end series of other brands. Using same series of speakers with any brand will have subtle notable differences and going with same series of speaker does not make sense as good upgrade . Also Going in highline speakers demand more power , which AVR cannot justify any day. Finally it's boiling down to the equipment upgrade.I also disagree with you on changing speakers part. Changing the speakers would bring you a considerable difference to your table tonal wise, imaging wise, depth and sound stage wise if those speakers are properly set up.
Every speaker is so different that a KEF can never be a Klipsch nor you can't expect a Klipsch to be transparent as a KEF or Maggie.
What i am telling is ,Power Amp may not be very essential for first time users . When you want to upgrade your HT or music listening to next level Power Amp is one of the essential equipment to consider , where you will feel more difference in clarity and punch .
Once you hear your speakers with power amp , you wouldn't want to go back with direct AVR outs for sure.