Cheaper access is good, open access is even better. Winning this fight is worthwhile on it's own and it brings open access closer.
And we're not even talking yet about the wealth of legacy articles locked behind paygates. Someone, or some legislation, needs to set them free.
I'm a member of the ACM and the IEEE, and a lot of other people are; it doesn't seem to me that the modest dues are significantly hindering progress in the field. If, due to some unexplained fortune, the ACM and IEEE were to drop their paywalls tomorrow, and grant free access to all, how much would really change?