Speakers are electromechanical, hence differnt sonic signatures.
Two different tweeters, mids operating in the same range is akin
to listening to two different female vocalists live singing the same
tune simulaneously. Is it bad? no, but I wouldn't want to hear
it that way all the time. Mixing two sonic signatures is counter
productive as you want your speaker to have a specific personality,
not the Borg - where there are 1000 voices speaking at once. You
can do this, but the chaos might be information overload for your
brain and you may get fatigued. Sometimes is just better to eat a
nice piece of steak with salt and pepper cooked on an open flame
than to add 50 spices to it.If you want to create a different sonic signature from the
loudspeaker, then create different ones by using your EQ and
crossover to alter performance, and you can always revert back
to a normal configuration too.