I personally offer my monitors a little variety, but always whole prey animals. There`s nothing wrong with offering inverts, but there are more nutritious foods, rodents being one of them. I`ll make a guess and say you add supplenments to the inverts? The rodents don`t need that, they are a "complete" meal in themselves!
If it were my monitor, I would feed mainly vertebrate prey, and some inverts too.... You can also offer fertilised quail eggs now and again, just break one over a rodent, or feed as is.