In my opinion, two forums that could definitely be merged are General Discussions and Members Only Discussion. The big difference between the two is that Members Only is used for more personally sensitive posts than the publicly accessible General. This is really false security. Anyone on the Internet can easily register as a member of WrongPlanet.net whether they have an autistic spectrum condition or not. If they really wanted to read our private posts for their own twisted sense of humor, they could.
On the other hand, I disagree with your suggestion to merge Television and Entertainment with Arts, Crafts, Writing, and Music. I occasionally read the Arts forum, but I never read the TV one. The reason is entertainment is not the same as artistic expression! I have no interest whatsoever in the latest reality TV show, the next Super Bowl, etc. In my opinion, this forum could be merged with Games, Sports, and Fitness to form one leisure and entertainment forum. I would advise retaining the Computers forum's separation from the other Special Interests boards because computers are one of the most common interests for aspies.
Honestly, sometimes the only forum I read is General Discussions; and I rarely work my way straight down to the bottom. I often choose to place my topics in General Discussion because I know fewer people read the other forums even if they may be more topical there.