If you already have active admin setup with a lot of things built on it, I wouldn't suggest changing it until you needed to add new stuff, or it was falling short somewhere for you. No point wasting the dev time if it works.

I would love to talk to you more about what you have customized, and what all would need to be reconfigured to get started with upmin to learn from you if you don't mind sharing. My email is jon [at] upmin.com.