YES YES YES THEY ARE SO WORTH IT
I started a series of short promotional vids last year, and it's been great. When I started, I didn't necessarily intend for them to be 'promotional', I just wanted to do something fun in a new medium. But I never pass up an advertising opportunity, and the traffic on the vids has brought lots of new traffic to their parent webcomics.
Just make sure you're doing what you do best, no matter the animation quality. The highlight of my series (it's a fanwork) is comedy and references to the canon, sometimes with 4th wall breaks. So if I deliver on that, no one cares if my highest framerate is, like, 2 fps.
Yeah, it's just barely animation; no voice acting, either. XD But my first video will be reaching 100,000 views pretty soon, so I must be doing something right.