Jack, your style of photography is very different than mine (BIF is a very small part of what I do. Even using telephoto isn't a big part), but for me, I would have to see a significant upgrade in IQ for me to consider adding a crop body to my kit. I just didn't find that I used my crop (my last was a 60D) after I switched to FF. The latitude for post work in FF images (particularly from the 6D) is just so much better.
Anyway, here is an image from the 6D in the opposite direction - this is a handheld ant macro with the 100L Macro IS lens:
Face the Sun by Thousand Word Images by Dustin Abbott, on Flickr
Great picture! You broke the rule of thirds and yet I like it. So what did you do? I am guessing it is the orange and black contrast that gets my attention.
That helps, but this image demonstrates the importance of using negative space appropriately. In this image the amount of empty space creates more visual interest in the subject that is present. On one of the file sharing sites, someone wanted me to straighten the horizon, which to me would actually diminish the image as it would remove the sense of the ant climbing.
One advantage of leaving negative space in an image like this is that this will make (I suspect) a successful stock image because there is a lot of room for a client to use.