I was really liking this demo! It's nicely produced, good levels, you have some real character in these and it was pretty tight! But then it started to die out after your Scooby and Shaggy impressions. I didn't get a sense of energy from the rest of the demo and the recording quality of your Nixon was off. Lots of mic feedback and it sounded like you got too close to the mic.
In my honest opinion, I would throw out the rest of the stuff after the :57 marker. Keeping a demo short is key and there's plenty of good stuff on here! But cutting that stuff is your choice. Good job either way!