Thank you, Julia. Your explanation was very helpful, and seeing the context about which I was asking by way of examples was particularly enlightening. Coincidentally, the exact meaning and use of "so" in this context is also used in Hebrew (I am a Hebrew speaker), so I now understand how and when to use it.
Someone once told me that Germans are less demonstrative with their hands and their voice inflections for expressing emotion as compared to, for example, people in the Middle East. However, emotional expression through the use of vocabulary is more acute in the German language than in many other languages owing to the use of filler words, such as "mal", "ja" and "doch". Whether or not this is true, the context of "so" in the example: "Und ich bin gespannt, was Matthias so zu erzählen hat.", appears to fall into that category as it does not change the meaning of the sentence, but reflects more the mood or attitude of the speaker.
Thank you again for your explanation. You continue to be an important part of this course for me regarding points of confusion:))