What I’ve learned in 5 years of running a SaaS
I just upgraded my laptop from a 4 years old mbp to a brand new one, got a 27" second screen display, and i can tell you my productivity has been skyrocketing. 
Performance gains are obvious, but the psychological aspect is also a factor. After working for a year on the same project, new hardware can bring some new joy, and a new boost to your project.