Nice tool jgrahamc. You should consider expanding how you detect/show diffing of the response bodies, since that has a lot of applications: detecting content changes, detecting ads/malicious code, detect crawl duplicates, security audits. etc.
Years ago I found the Levenshtein distance is super helpful to determine how different the responses are, and used it as part of a black box web security scanner. You can do this just on the Raw HTML, but that's noisy and shows a number of differences. It's better to use an HTML-aware string distance function, that diffs just page content. I used that a channel for detecting blind SQL injection (in combination with some other things).
I also found that you can go a level higher, and use Levenshtein on just the HTML tag structure of different responses. By looking at page structure, and applying different weights based on the HTML tags that were added/removed you can group similar pages, which usually maps to the different functional areas/templates of a site. As in, you can say "these 5 pages are all product details pages", "these 10 pages are all blog posts", etc. Super helpful from a security scanner, since this could inform crawling/auditing choices and speed up audits. It also allowed us to say "you have a XSS vulnerability in your Blog comments form" instead of just saying "you have XSS vulnerabilities in these 100 pages".
Anyway, there is a lot of value in detected how different/similar various responses are. See some of Google's published work about detecting near duplicates for web crawling...