I justified my purchase by the fact that I'm showing to Google that I'm willing to pay for privacy; there's no doubt that Google is paying attention to the amount of GrapheneOS users. In fact I would pay extra for Google products if they offered their products free of advertisement, scanning and with E2EE.
Also GrapheneOS is a lot more than just about privacy. It's one of, if not the most, hardened mobile operating system the average consumer can use. That gives me a lot of peace of mind when using my phone.