In my experience open mics are not simply for musicians.   I go to folk clubs but also find the open mics a valauble place to go and get experience or try out new material. I'm a storyteller as well as a singer and find that song/music venues are not always accepting of what I do. I also go to venues that are literature-oriented. There is a growth right now in poetry readings and allied literature activities. My stories go down very well at these venues. It probably helps that I've had training and am now starting on paid bookings so my work is of a good standard. Songs and music go down well too. I find the standard is variable but there are some very good performers out there in these open mic slots.