I've seen more than one Grandmother's Flower Garden flimsy at the thrift stores, and adopted one myself. I think it is the finishing decisions that throw most people off, or the goal was to use up fabric and not necessarily end up with a completed quilt... My top was HUGE and still is even with taking out a number of blocks. What I've decided is that I will keep the borders scalloped with the big hexies coming in and out, but that I will trim the small hexies to straight lines.
One idea I rather liked for finishing this sort of project is to sort of applique the hexies to a straight band on the edges. Then if you do want to make your top larger, it is easy to add a border, and if not is a nice straight edge for binding.