If you want to attract more users/members of Mudcat, one way to do it would be to encourage owners of other sites to post links to Mudcat.

How about this: Every time you go in search of lyrics and find them at another site, e-mail the owner of the site and thank them for making the lyrics available. Tell them that you intend to post a link to their site at Mudcat, and suggest that they might want to reciprocate.

Here's an interesting exercise: use www.mudcat.org as a search argument in Google. Then you'll see this result. Follow up the links on this page to learn who mentions Mudcat, who links to Mudcat, etc.