Whackmnstackm,
First - THANK YOU for your service Sir!
I first joined the NRA in 1962 and have never regretted it. Being an annual member isn't that expensive, a good alternative to life membership, if that fits your budget.
Yes, they will ask for more money. They need to, that's how they are funded. It's a simple thing to just throw the envelope in the trash when you receive it and don't want to send anything more than your dues. EVERY organization that I belong to asks for more money. Heck, in my church I am one of the people who ask others to give more too. If you don't want to contribute more, ignore it. I certainly can't respond to every plea I get for more money either. Being a member is enough anyway. We need you. (You won't receive pleas twice a week from the NRA as was indicated above either. That is just hogwash.)
If there was ever, ever a time when it was more critical to have a strong NRA, I can't recall it. I'm glad I'm a member.