Like all things, it depends on if you use it, and how much. What’s landing an account worth to you? LinkedIn Sales Navigator, et al, is about $1,000 per year — will it help you close more than that? If you use it, probably. But if it’s just another shiny thing that sits idle, then it won’t be that useful.
We've heard mixed experiences with Sales Navigator. It does help a lot on researching the customer's org structure / understanding the org. If you're specifically looking for Org Chart, check out DiscoverOrg.com. The search is also powerful, and allows for a more granular search, but it's not so great on the direct message responses.