The best mod by far is to use strapping tape (or clear packing tape if you must) and run a strip along the entire bottom of the fuse, on either side of the nose, and a couple of strips down the side of the fuse near the tail. This stiffens it up greatly if done correctly. You will no longer notice the wiggle when applying rudder inputs and it makes it much more durable. The best part is that it will come off with little/no damage if you have to remove it. It will take the paint off the wings though. I also ran a strip of clear packing tape under each wing where the carbon rod is inserted and beyond the end of the foam plug. I did this because the glue holding the plug and the rod in place was giving way, but it also stiffenned up the wing greatly so high-G. loops are more stable and less hectic.
When broken..just piece it back together. I use a hot glue gun sometimes and it holds up very well. The best glue I've used on foam so far is Gorrila Glue. Only use a little, tape it together till dry and follow the instructions. GG is very strong, weighs next to nothing, and fills in cracks and holes as it expands.
Barlowe, I think you are over thinking it a bit, and the weight would be significant. Just glue a new chunk of foam on it if it's really that bad. The best thing about foam parkflyers is that they are easy and cheap to fix (usually). Sorry for the LONG post. I hope it helped a little. Good luck!