I do realize that backlinks to URLs disallowed via robots.txt do still have whatever Google's modern version of pagerank is. Depending upon how many incoming backlinks there are, even if Google can't crawl a URL, it might use those external signals to still rank the URL in the search results (albeit with no page title or description).
My question, however, is whether the domain overall is helped? I suspect URLs that are unable to be crawled can't spread pagerank to other pages. By any chance does the domain root get a little lift up? Or does that pagerank completely evaporate at the URL level?