I don't think this is quite fair on the NRA's part, at least not today if it once was in the past. In the 2000 general election, 48% of the people that showed up at the polls owned at least one gun, a number far out of proportion to the ratio of owners/non-owners in general. And while the RATS were concerned with all sorts of other things, almost all of that 48% considered "gun grabbing" to be at or near the top of their list of concerns. It is because of these voters, whether they belonged to the NRA or GOA or any pro-gun group, that caused the RATS to completely drop gun control as an issue in 2000 because their internal polls showed very early that the 2nd-Amendment crowd was huge, angry and ready to vote out anyone they considered to be a threat to their rights. And in the end, they did. It is also because of these voters that gun control has been repealed in so many states and why so many new CCW laws are coming around.
In the end, it doesn't matter so much whether you send the Salvation Army a $10 check ever few months as much as it does when you actually show up at a Salvation Army center and volunteer. Likewise, all the subscriptions to the NRA mean nothing unless people get off their butts and get politically active.