"And yet the liberal Catholic churches don't seem to be able to grow substantial lay membership"
It strikes me that this about "disssident" rathaer than "liberal" Catholic churches and I would list some of the various "Anglican" groups among the more successful of these in recruiting members. They see themselves as broken away from the Episcopal Church and are more "High Church" and closer to the Catholic Church in my experience. I am also somewhat familiar with the "Antiochean Orthodox Church" which seems more stable in organization and membership. 
While I remain a loyal Roman Catholic I recognize the essential fidelity of these groups to the doctrine and authority of the Catholic Church and wonder if we are not being led by the Spirit to accept them under a broader umbrella as the "Christian Church".