They have to try new stuff. Re-tread syndrome has killed alot of franchises. I think the CGI movie will be great, it'll definantly do wonders for the fanbase, but I don't know how much money it would make.
I think CGI is the next logical step for the TMNT cartoon's evolution. No ofense but the animation quality on the old toon was pretty horrible. CGI will look alot better and gather alot more atention then just a normal toon.
I'm also looking forward to both the movie and series being alot more darker and comic-derived then thier predocesors.