I believe that it's totally worth it if you want great video. A lot of people say "buy a video camera) but the fact is that these newer dslr's that shoot 30fps 1080p video are shooting with video quality that it would take $10,000 to get with a video camera. Have you ever saw a full video setup with a 35mm adapter? They can be huge. Here's an example of one that is actually not that big. http://www.bhphotovideo.com/images/35mmAdapters-1.jpg
I'm not aware of how much experience you have with video, so just to put it out there, 35mm adapters let video camera's get that nice shallow DOF that dslr's already have. And you can adjust the DOF on a dslr by changing the lens or the f stop on the lens.