Your own example shows how running empower that way is a mistake. It is right by the rules, but if interpreting it that way makes empower [+2 spell levels] stronger than maximize [+3 spell levels] for dice plus level based bonus spells then I fell there is a mistake.
Yes, but what you are explaining is more along the lines of why empower should not multiply the level-based constant bonus, not so much as to why it would not apply.
By the rules (as the magic missile example in the PHB has shown beyond reasonable doubt), you first add everything together, then multiply the final result by 1.5.
This is because 1d6+1 is simply the game's way of saying "any random number between 2 and 7". If you allow a player to take a blank 6-sided die, paint the numbers 2-7 on it instead, roll the result and then multiply the final number (which will be anywhere from 2 to 7) by 1.5, it makes no sense why the same treatment should not be given to "1d6+4". The designers likely only broke it down into the XDY+Z layout so we can easily arrive at the desired results using dice we own (d6s, d10s etc), rather than having to waste resources procuring customized dice.
I would say that empower is only situationally stronger than maximize. It appears that empower would be superior when applied to spells with a flat bonus (such as ray of enfeeblement). Conversely, if the spell in question involved only dice rolls (such as the myriad of direct damage spells like fireball), then maximize would deal more damage (and also has the side-effect of speeding up gameplay, since you don't need to roll any dice).
