I'll do the best I can, which is take you directly to the source:
https://support.google.com/webmasters/answer/76329?hl=en
"Consider organizing your content so that URLs are constructed logically and in a manner that is most intelligible to humans (when possible, readable words rather than long ID numbers)."
That's fairly clear and exactly what you're trying to get at. This article is a direct piece of the "Webmaster Guidelines" section - and should be followed where possible. This should be enough to get you across the line.
I also think most SEOs would agree that Google uses keywords in the URL to at least some extent. We know they use search with synonyms and related keywords. So if your URL contains /seo/ it's much more related to "seo" searches than /123/ is. So yes, it will help. It's hard (impossible) to quantify by how much though.