I don't know what value [the RPGA] has to Wizards of the Coast aside from the obvious (but not obviously meaningful) concrete numbers of active
D&D players they can provably claim, but since I have no interest in playing in or running "public" games, and don't see much point in reporting my "private" gaming, it's pretty irrelevant.
I would be interested to know what value the people running it believe it has beyond providing those concrete player numbers for annual reports to management.
This I read as two separate questions. The first is what benefit does the RPGA provide to players, particularly those who don't play "in public." Let me answer personally first.
When our daughter was born in 2001, my wife and I decided that we needed a hobby to help us have some time for ourselves--as my wife would be home from work and has the tendency to get a bit stir crazy. We'd played DnD for years in high school and college, so with the release of 3E, we thought we would give it a try again.
Unfortunately, there weren't a lot of players in our area running home campaigns, but playing with them wasn't feasible for a variety of reasons. I'd run dozens and dozens of home campaigns over the years, but I now had no time to do all the prep work with job and family and other obligations. This was when Living Greyhawk was getting started, and there were some semi-local players holding game days and conventions, so we thought we'd give the RPGA a try.
Perhaps we were just lucky, but our first experience was wonderful. The DMs were great, which made the adventures fun. The other players were a mixed bag, but we were able to meet players who shared our interests and situation, and from that we were able to put together regular home games. But since schedules of the players was so erratic, the setup of the Living system was perfect. People could show up or not, because we had a group of people to draw from. People who missed games could make them up by playing them elsewhere and still be on the same page (and roughly the same level) as the rest of the group. I know many RPGA members who never attend public events. They use RPGA content for their home games, free of charge, and are very happy with it.
Now on a more personal note, I did find some of the RPGA rules and regulations off-putting, and some of the adventure writing was weak. So I got involved. First is was just volunteering to do some work for the LG Triad for my region, and one thing led to another. It was a great deal of work, but I was able to ultimately get my work in front of people at R&D themselves. And now I have my work on bookshelves. So what did the RPGA do for me? Only give me the opportunity to pursue and fulfill one of the my childhood dreams.
The second question you seem to ask is what does WotC get out of the deal. Perhaps to start I should note that the RPGA is more than just Living campaigns. All of the D&D Worldwide Game Days are managed through the RPGA. Much of the playtesting of the 4e rules was done through the RPGA. Some of the content the RPGA provides is aimed at giving local game stores a way to draw in business, thus keeping gaming healthy and growing. I would say that "concrete numbers" are probably one of the least important things the RPGA offers WotC. It is more like the RPGA offers WotC an organized and reliable line of communication to and from a large, diverse, and motivated player base. At DDXP and GenCon this year, I got to watch (and even sit down with one of) several WotC staff members as they ran games in the RPGA area--both longer 4-hour adventures and shorter delve-style events. I don't think I am exaggerating when I say that doing so was fun for the players, but an incredibly valuable and eye-opening experience for WotC staff. The value of seeing how players are using their rules in a controlled setting, seeing what questions came up or what rules were misused, is something they can take back to their desks and meeting as use to improve the game. I played in a 17th-level game run by Mike Mearls, and I can say that there was a great deal of discussion about rules, and a couple of times Mike seemed surprise by rules assumptions that we were making.
The RPGA keeps data on how often and what types of games people run. This can allow them to contact certain people and gain insight into play experiences. They know that Bob runs a game day every Thursday that usually seats 8 tables of players and DMs, most running adventures of levels 7-10. They can contact Bob directly and say, "How many people are playing x or using y? How are your DMs handling this rule?" It is more than numbers.
Oh, and you get free swag for being a member and/or being an RPGA DM: Andy Collins' 4e-updated "The Village of Hommlet" adventure for signing up, and this period DMs got ship-based Dungeon Tiles. It's a small thing for some, a big thing for others, but both products were excellent to me.
While I am obviously a big fan of the RPGA and an administrator in one of its current campaigns, I need to be clear in one thing: it is not for everyone. If you are only running home games and have a solid player base, if you create your own content (or if you are content with buying adventures), and if you don't want or need to interact with WotC or the gaming community as a whole, there really is no need to join the RPGA or worry about it. As long as you are having fun playing or DMing your games, rock and roll! That's why we all should be here.
Thanks,
Shawn