Country club memberships can rarely be justified on a “cost per round” basis. It’s all about the access. And the fact that you WILL play more regularly because the marginal cost of playing is effectively zero.
That may not be a big factor for you personally, as you seem to get out a lot anyway. But what makes it a no brainer for me is your kids. They won’t play nearly as much if they don’t have the access that a country club provides.
And you live only 5 minutes away? And the cost is so low?
Do it. Do it now.
(Some people will say they appreciate the variety that comes from playing different courses all the time. And I don’t disagree. But I actually love playing the same course repeatedly and the challenge that provides. Golf is more fun for me when I have great course knowledge. I wish that club had 27 or 36 holes for you, but that’s not the end of the world.)