There are secrets you are sworn to protect, yes. But not everything that goes on behind closed doors is a secret.
This. Exact. Thing.
I don't think our numbers are dwindling because of a lack of secrecy. I think it's more because Masonry skipped a generation. Sure we had a huge influx in numbers, mid-20th century. But the baby boomers skipped out and now it's returning to pre-war Masons/Population numbers. My lodge certainly is losing a lot of members to death, but we're also taking on a few EA's every month. If you want Masonry to grow, you have to do more than just guard your secrets closer. There are countless discussions on this forum on how to do just that. There are countless resources available online with more theories than anyone could read in a lifetime. None of them espouse the idea that keeping every minute detail a secret, even our dues, is the way to go about that.
Now, about the secrecy. I grant that secrecy must be maintained. Where we are to draw that line is where I, and many brothers here, disagree with you. Things that I absolutely keep secret: our modes of recognition, what happens in our degree ceremonies, meanings of our symbology, the catechisms, etc... But if a man walks up to me and asks about Freemasonry, I don't respond with "It's a secret. If you want to know, you have to join." If you do that, he'll go online and google it and end up in the hodgepodge of conspiracy sites, clandestine lodge websites, misinformation sites. He'll probably click on Image Search and see the illustrations from Duncan's Ritual. Whether or not he spends the time sorting through it all and making up his mind, or spends the time to connect the dots and understand what the pictures means, depends on the man. But either way you've lost a chance to have a personal conversation with a potential brother, and give him honest answers about what Freemasonry is and what it means to you.
And one of the questions he will ask you is what your dues are. It's no secret, nor should it be. The form of the lodge may be a secret, but that doesn't mean you can't open your doors before a meeting and let a man and his family see the lodge room. If someone takes the time out of their life to come to our lodge and consider joining, we take the time to show him around, encourage him to bring his family if he has one. We show them the lodge room. We explain there is always a Holy Bible on our alter during our meetings. We show them where the officers sit. We show them our wall of pictures of our past masters. We answer any questions we can. And if they ask one that we can't answer, we tell them then, "That's one of the secrets. You'll have to join if you want to know that." And then laugh and do our best to give as much of an explanation as we can without violating the obligation.
I agree you need to take the craft seriously, and hold your lodge in high regard. But that doesn't mean alienating yourself, or leaving interested men to find the answers on the internet. There are Masonic discussions you can have publicly without violating your obligation. And this site is one of the best places to have that discussion.