I've never owned a copy of Roget's, and now I'm curious/tempted to get one, but my go-to digital word picking assistant has always been OneLook Thesaurus: https://www.onelook.com/thesaurus/
Hey, I'm the developer of OneLook. I'm so glad to see it here!
The concept clusters on the site are directly inspired by Roget's work. Like the author, I see a thesaurus less as a synonym dictionary and more as what the word literally means, a storehouse of treasure. I'm in the midst of a long-overdue data refresh across OneLook right now, so I'd be curious to hear your feedback once it's done.