Yes, in my experience producing over 700 explainer videos with my company (www.Gisteo), higher quality videos convert more.

Importantly, however, it's the script first and foremost that dictates "quality." Think of the script as king, visuals as queen or maybe even prince :)

I'd much rather have a compelling script with so-so animation/imagery than a mediocre script produced by the finest animators at Pixar. The story is what sells. Eye candy is more of a nice bonus....it can never be the other way around!