A lot of those other sites are interesting to visit, but Free Republic is the "home" site that conservatives return to. As far as the falling numbers, I hate to say it but I sense a certain malaise (or boredom?) that may be coincidental with the final years of an eight-year Republican Presidency. I have a feeling things will heat up again when the campaign season hits full stride.
I agree with Lancey Howard's comment. FR is home. I check in every day, and I visit the other sites occasionally. The only other site I visit every day (except for business sites) is Drudge so I can see what is going on with the disfunctional celebrities.