Great video. I agree with all the points you mentioned.

• I don't like it when the title of a video and the text in the thumbnail are exactly the same. There really isn't any point to that. The text in the thumbnail should complement the title (or coexist as you said).
• It usually looks bad when someone just adds text without any drop shadow, outline or background banner. For example, If you just put yellow text on your snap, it will probably look like shit. It would be better to outline the yellow text with black or to use a complementary colour of yellow such as blue. That helps the yellow look more defined.
• I find adding more contrast and saturation to a thumbnail makes it look better. The thumbnail needs to stick out. Without adding more contrast, the picture looks flat. Without enough saturation, everything looks dim.
• Too much text is a no go.