The thing with wider reading, is that it's not just about name dropping (and accademic publications are prefered anyway). You have to reflect on what you've read, and why it interested you/furthered your desire to study economics. I don't think you could effectively do this with a tweet. You also don't want to alienate the admissions tutors, which you might do if they were very traditional. As economics is a competitive subject, it would be best to just stick to more traditional media.