The difference between the power out put between 100 and 200 wts, everything else being equal, is 3db. If that is the threshold where you and distinguish clear differences in SPL's then you are correct. But if you have the ability to discern smaller changes (and I think most do - some even claim to her differences as small as .5db) then your conclusion wouldn't work. You might see how manufacturers treat this issue by looking at the different gradiations they use in the steps in the attenuators. Some use 1db, some 2db, and some use gradual decreasing step sizes as you 'apply more my volume'.
So everything else being equal, the difference between 100 watts and 200 watts is a mere 3db increase in SPLs. When you are listening to your system with the volume turned up, and your max'ing out your systems (including your room) ability to produce coherrent sound, a 3db increase in SPL may be relatively inaudible.
If you haven't already done so, buy a SPL meter and see what average/peak levels you listen to in your room and do the math. But don't be surprised when you find that with even moderately efficient speakers, that you rarely, if ever, exceed say 20wts, and even then only on peaks. And if you do, consider that if you are listening to music at that level it may not be a problem for long.
Nothing wrong with 'powering up' but the price go's up as well and its a lot to pay for something you may not need.