For some people it will be worth it - for others, it won't.
Ribe is the oldest town in Denmark, thus having a lot of history. But, it's home to just over 8000 people, so it's not big.
I think Ribe is worth a visit if you can appreciate the old centre, church and the history of the place - like the poles marking the water level at former storm surges. If you are in the area, you could rent a bicycle and go for a ride in the very flat landscape (maybe to the levee facing the Wadden Sea).
When you have a week, I would spend a (couple of) night(s) in Denmark beyond Copenhagen. Copenhagen simply isn't representative for all of Denmark. If you're not sure Ribe is the right town for you, there are plenty of other cities, towns or small islands to choose from.
I won't comment on the Viking Museum in Ribe, as it's been many years since I've been there, so I don't remember it that well, and things may have changed at the museum since that time.