How does "Much Ado About Nothing" engage the head as well as than the heart? How can a romantic comedy appeal to your head?
The simple answer to your question is that the play operates on several levels at once.
There is the romantic comedy which appeals to the heart, and not to the head: the heart-warming stories of Benedick and Beatrice and Claudio and Hero.
But the play is also more complicated: it operates around a non-event - an event which does not happen - Hero cheating with Borachio. It really is "Much Ado About Nothing".
"Nothing", of course, was also Elizabethan slang for the female genitals. So the play might be read as "Much Ado About Vaginas", and appropriately, most of the plot hinges on the men trying to get the girls.
"Nothing", in Elizabethan dialect, also sounded exactly like "noting", or overlooking (taking note of). The two gulling scenes - as well as Don Pedro and Claudio's (offstage) viewing of Hero at the window - demonstrate the way that the play similarly is structured around noting, overlooking, and watching.
Yet in each of these cases, the observers are watching "nothing". Claudio does not see Hero cheat, Benedick and Beatrice do not hear real conversations. It is fake - like the theatre that the audience watch when they see the play. How, then, can we watch "nothing"? What does "nothing" mean? Is the play really "Much Ado About Nothing"?
Look at these questions, and you see that Shakespeare is the master at stimulating your head and your heart at the same time.