Retrospect the Retrospective

Instead of assuming that Retros are working for your team as they are. Review them like you would a Sprint. Asking questions like -

What do you get from the Retros?

What one thing would you add to the retros?

What one thing would you take away from the retros?

I believe it's important to remember that scrum is a lightweight framework, and you should be reviewing every aspect to ensure it is best tailored to your team and the work they are doing.