Indeed. It does seem fairly obvious to improve upon character design, but it’s nice to have more concrete numbers. These data suggest that an absolutely amazing character design can contribute as many as 3-4 points to a game’s overall score, which is far more than I would’ve expected. I think there definitely is a “feel good” factor here. We tend to empathize with characters that are more like ourselves and, well, it’s hard to empathize with an abstraction.
I agree with your thoughts, but I would actually modify your fourth point. Instead of making clear instructions, try to make a game that requires no instructions at all, or 2-3 lines of text, at the absolute maximum. If text is absolutely necessary, then include any text instructions in the first few seconds of game play. Most players won’t read instructions and, even when they do, instructions tend to be forgotten very quickly. (FWIW: I’m an academic with a background in psychology, robotics, and user interfaces, so I’m pretty darn familiar with training, memory, and attention as they relate to conveying information in digital media.)
I agree. Fortunately for the analyses presented above, the bias you mentioned would only apply to the correlation / regression found between 's scores and the chat scores. In psychology, the bias you’re referring to is called Anchoring (or Focalism), and it can be a powerful tool for negotiation. Unfortunately, I don’t have the necessary data to estimate the potential effect of the stated bias. 
However, because AllarScore was the only dependent variable used in the second regression and the multiple linear regression models, ChatScore would likely have had little-to-no effect on the relationship between AllarScore and the other variables analyzed. Unless, of course, the chat piped up and offered a score before , potentially biasing him… but it seemed very rare for chat to offer a score first, based on my observation of the stream.
Oh, and thanks! I’m glad people appreciate these statistics.