If you look in my gallery you can see how I reinforced the upper frames.
I would definately do this! I had one set of upper frames which broke due to vibration fatigue from a set of bad main bearings.
Miniature aircraft says that the upper frames must be reinforced if you are going to cary a heavy load (camera equipment).
I have heard of people simply purchasing two sets of carbon upper frames and using two of them on each side, thereby doubling the strength. I don't know if Miniature has approved this method.
I did show Miniature my aluminum doubler plate and they said it shold work just fine. Or you can order the aluminum upper frames from them if they still have them available.