Mike,
The Fried Egg Podcast has 2,472 followers out of 25,000,000 golfers, generously rounded to 0.01%.
I couldn't quickly find the following of the Tartan Talks (subject of the OP) but their parent magazine (and my former editorial outlet) has about twice that many followers, presumably within the golf industry given their subject matter.
I haven't kept track (and have no way of doing so) of the sales of recent gca books. I do know that many of those gca books in the 1990's only sold about 3,500 copies each. The Golf Course (and several editions of The Architects of Golf supposedly sold close to 100,000.
Tom Doak's Confidential Guide sold 12,000 copies and probably would have sold more, had they been available. Getting to 18 was a limited run of 1,500 copies. Doak's Little Red Book has been discounted, indicating a possible overstock.
The math side of me always wants to double check vague words like "a substantial number." Even if the combined sales of the Confidential Guides old and new were close to the Architects of Golf, 100,000 is only half a per cent of golfers, maybe 1% if you figure two people had read every copy sold.
I would love to be wrong in this case, and it makes sense to me that more golfers than those who subscribe to podcasts or buy books are now "more aware" of golf design via various outlets, including having the architect's name on the scorecard. However, as I mentioned before.....not all of us spend a few work hours per day on a golf course architecture site, so we may not be the ones to ask.
As to your other contention that most golfers don't know their course is boring.....that one would be an interesting theory to test out, although it would take suspending our view of architecture and seeing it from their perspective, I suppose. I'm not sure we could!