I’ve gotten by without the expansions so far, so I don’t know if “need” is the right word for the expansions. That said, they do enable some new areas, equipment, and gameplay modes, so I’d say they definitely offer value. It depends on whether you think you’ll exhaust the vanilla content.
I mean, I’d be tempted if I wasn’t already trying to work through my very large backlog of things I bought during last year’s holiday sale.