The functionality of the CTA buttons seems to be pretty limited. You cannot overlay an image on to the button, such as an arrow, and you cannot increase the size of the button without adding more text. In my opinion the CTA buttons should have the same functionality as the 'Divider'. It would be great to have that kind of control of the height and width of the button.
We wanted to follow-up on this thread to share the good news that our cross device templates do allow buttons with rounded edges! In the meantime, please feel free to continue commenting with further examples of customizations. Or even vote on any of the other open ideas to let us know what you would like to see.