Federico, thanks for writing this. There is a mixture of hope and despair in the responses, as well as an understanding of the complexities in an all-volunteer site.
The content in Mutopia is substantial enough to be a great resource and managing this content via volunteers will always be a challenge. There have been a number of updates in the past year -- utf-encoding conversions, project status updates, data consistency repairs -- and these have been good starting points. Much of that effort took place without engaging mutopia-discuss and that was probably a mistake.
As long as the content is good (correct, aesthetically pleasing, readable, and using a reasonably current version of LilyPond) I believe the site holds value. It is not as good as it could be.