CEA and GiveWell are both building communities, GiveWell to the point of more than doubling its community (by measures such as number of donors, money moved, with web traffic slightly slower) every year, year after year. Giving What We Can's growth has been more linear, but 80,000 hours has also had good growth (albeit somewhat less and over a shorter time).

That makes the bar for something like CFAR much, much higher than your model suggests, although there is merit in experimenting with a number of different models (and the Effective Altruism movement needs to cultivate the "E"/ element as well as the "A", which something along the lines of CFAR may be especially helpful for).

ETA: I went through more GiveWell growth numbers in this post. Absolute growth excluding Good Ventures (a big foundation that has firmly backed GiveWell) was fairly steady for the 2010-2011 and 2011-2012 comparisons, although growth has looked more exponential in other years.