I've been thinking about becoming a member for years - never have taken the final step. To me, the value isn't there. The discount is lost if you can't attend a game or two and the extras aren't making up for it. It is currently pretty easy to just buy tickets to the games I attend and I can spread the cost over the year rather than a lump sum up front.
Just a few little things could really make a culture of membership in the club and make you want to do it. Treat members like something a bit special. Hand out some more banners/scarves/hats whatever. Show a little bit of attention to them. I haven't got anything off the top of my head, but it isn't my job to come up with it.
Basically, for me, paying a lump sum up front with the chance I'll probably miss 2 games a year isn't worth becoming a member. If games themselves felt different as a member, I would jump on it ASAP.