Loving this more with every improvement. I had good effect on my balloon a few renders back by doing a Merge with the Default and a Glass shader and set it to add; you might want to try that. Worked well with the sun in a position similar to the one you have but I went for the sun thru the balloon in mine.
Reading and watching what everyone does is where I got my idea (stole yours) for my fountain spray, bobby. That balloon is fabulous!