Even though I have never submitted a reader review myself, I know a few of the members of the board who have. For them, so it seems to me, that is a pretty big deal to have one of their reviews selected for inclusion in the reader reviews section of the site.
I think one of the main differences between the reader reviews section on the site and the same on the message board is that anybody can submit a review to a message board and get instant gratification on having it published, but it is a special badge of honor to have it included in the reader reviews section of the site.
Another thing which is different is that the reader reviews are attached to their actual names while most of us on the message board use pseudonyms or nicknames (for instance, Scott
's real name is Cletus Clowpepper
An alternative might be to use the message board for all reader review submissions as you suggested, but also add a sticky to the forum with guidelines on writing a review in BadMovies style. If someone happens to post a really good review, that would provide you with the opportunity to add it to the reader reviews section of the site, and it would be like a reward to them for a job well done.
Redirecting the submissions to the board, as you suggested, might also have the added bonus, for the board anyway, of a potential addition of activity and/or membership on the board. (heh...heh...more victims...uh...scuse me..
Ma two cents worth anyway.