Contrast in Text Composition

I'm currently reading a fascinating (to me at least) book on history -- Weird History 101 by John Richard Stephens. However, one of the annoyances I'm finding in this specific printing of the book is the lack of contrast between the main narrative and the quotes, letters, and other items which make up large parts of the telling. Pages are set in two fully-justified columns with a serif typeface. The letters and stories from other sources use the same typeface and are indented on one side only about two characters -- barely noticeable. Reading along it's sometimes unclear when the book's author has taken up his narrative.

There are other sidebars or interesting tidbits inserted throughout that are set in italics and set apart by rules. But it's those usually long, barely indented passages within the rest of the text that often make it hard to follow and know who is speaking.

A larger indent -- on both sides or a change in font for these third-party letters and stories are some simple changes that would make it much easier to follow.

Read more on contrast, reader's cues, and book design:

• Visual Signposts, especially indents, bold/italics, leading
• Contrast With Type
• Margins in Page Design (this particular book has fairly generous margins. Perhaps narrowing them slightly would have allowed more room to indent some of the passages.)
• John D. Berry on Book Design, focuses on text spacing and typeface selection
• Creative Indents, looks at extreme indents, outdents, and using dingbats to separate paragraphs