Is more amp power always better...?

200-300 watts. For example: MC312

this is one of those "all things being equal" situations. where yes, more power is always better if the amps are otherwise equal. the reason for that is that amps sound better when they have headroom, meaning they are operating in their lowest stress point and lowest distortion point, which allows them to give the music ease and authority.

OTOH it’s rare that all things are, in fact, equal, between two different amps. some less powerful amps have simpler, more musical and refined sound than more powerful amps do for various reasons. so even though an amp might have an easier time with some speakers in some rooms, you cannot paint with a broad brush since amps circuits vary.

there are some obvious amp <-> speaker pairings in large rooms that are not going to work very well. so sometimes you really do need that more powerful amp. but your goal should be the right amp, not necessarily the most powerful.

one other important factor regarding amplifier and speaker matching for a particular room is the type of music you want to hear. if you want 'large scale' and 'very dynamic, complex' music to sound natural and not limited then more power is more significant. if you like small combo or girl with guitar mostly then amp headroom is not as important. if then later your tastes change then the system capabilities might need to change with it and you may need a more powerful amp, or an easier to drive speaker system.

IMO, Amp / speaker pairing is a tough nut to crack. So much comes into play. Listening preferences I think is a major factor that gets overlooked. I’ve had a 200wpc beast that didn’t sound good unless it was pushed to volume levels I don’t find enjoyable. Whereas on the other hand I’ve had 75wpc do the job rather well. Definitely do as much listening as possible before pulling the trigger. Good luck!

Type of quality power matters too.  It's not just about quantity of power for me.   

Rotating now between my tube amps to my solid state amps, for many years, formerly i used decent 200-300w dual mono Class AB amps. Nice full sound, yes. True Class A sound, NO.  I'm back to experimenting with this a lot again recently.   

Now trying the upgraded 50w Class A solid state amp again this winter. Its a bit more lean first 45m of warmup. Once its fully warm and toasty past 60m to 120m, the Class A 50w SS amp is more magical and engaging to listen to than my more powerful Class AB 200-300w amps were. Particularly at low volume levels too. 

Would I say the more powerful solid state amps sound better in this case?  No.  

There are days the Class A 50w solid state mosfet amplifier also puts my other two Tube Mono 100w amps to a challenge of sitting for a while longer. 

Lots of good advice here. If you can find an impedance graph for your speakers and see that they spend time at 4 ohms or below, you will want to ensure that the amp doubles or comes close to doubling wattage when impedance drops to that level. Another thing you may want to look at is how many watts of class A are available before A/B kicks in. But as many have already stated, specs alone do not tell the whole story, in the end it has to sound good to you.