The Mopidy Core API v1.0 and later, is not backwards compatible with pre v1.0.
Since a number of users use Mopidy in other distributions as well, Remotedy had to follow.
Yes, upgrading Musicbox to latest Mopidy is a good idea.
Currently v1.0.5 is the latest Mopidy release and contain a number of bug fixes since v1.0 got introduced in March.