I have mixed both in much the same way you described. I did an overall straight grid by machine and hand quilted a heart in each block. I have also done it with a baby quilt. Straight line machine quilting with my walking foot and the bear was hand quilted. Here is a link to the bear one.
http://www.quiltingboard.com/t-25770-1.htm
Regarding the cat paws. I recently did a childs quilt with cat paw stencils that I FMQ. I did a FMQ stipple around the cat paws and it hid a multitude of errors when following my original stencil, it also made the paw prints stand out quite nicely. Here is a link to that quilt.
http://www.quiltingboard.com/t-54829-1.htm