It is not possible to answer the "worth" question without knowing how many medieval cities you have already been to. CK is relatively hard to get to, but it was a high-priority visit for me - not necessarily for everyone. Rick, among others, mentions car services that provide one-way trips like yours for a substantial if not unreasonable price, if there's more than one person in the party. For one, it's a luxury price. We took a one-day car-and-driver trip from Prague to make the most of the day in CK. We were very happy with the visit.
Other people say that CK is 200 restaurants and 2000 hotel rooms. Take your pick. There are lots of things to see in Czech Rep. besides Prague, which is a great city.