In Mexico they say, "Peor es chile y agua lejos" (Worse is eating a chile pepper a long way from water).  Something is better than nothing.  An English club is not the same as having native speaking friends, living in an English speaking country, etc.  It is, however, better than nothing.  One obvious problem is that members may be learning mistakes from one another.  This is usually outweighed by the oppotunity to speak English in a non-threatening environment.  In a classroom sometimes every little error is corrected, and this destroys the student's self confidence and inhibits his speaking.

"Growing Together" in Curitiba is a very successful club, but much of that has to do with its excellent leadership.  It does a good job of attracting native speakers to its meetings.  People go because they know they will have a good time and see friends.  It has a varied program too.  In fact, it even has a theatrical group that puts on plays.