Yes, join. Yes, you will get a lot of mail from them asking for money, but you will also get a good magazine and help support pro-2A legislation. Toss the jun mail...
As others have said, they are not perfect, but they have the clout to actually make things happen. There are other RKBA groups whose positions I may agree more with, but a lot of people already consider the NRA to be right wing crazies. Hopefully as more good legislation gets passed, National opinion will move more to the point where the NRA can work to repeal some of the worst gun laws like NFA and such.