Your first GOS Pixel will have so many security and privacy changes that it might actually justify the investment. But you don't have to jump all in at first...
For me a used Pixel 3a was my first GOS experience, coming from a perfectly functional Xiaomi Mi 9T Pro which had better hardware in every regard. Within a few weeks I didn't want to use my Xiaomi anymore and ended up selling it.
The next upgrade was a Pixel 5 because I wanted a secondary device to separate my working and private phone experience and profiles didn't do the trick for me. From here on I was only buying new phones when the current one was end of life regarding security updates.
You'll have to decide what your priorities are, most people still use phones with security patches from years ago, others buy a new one every year to have the most recent features. Your solution could be to get a good deal on a Pixel 6a and try GOS there (if your funds allow for this approach). Use it for a few weeks and you'll know whether GOS is the right thing for you. Then you simply sell your flagship or the Pixel (after flashing Pixel OS back on it). You might even decide that the Pixel A series is more than enough and save a lot of money long term by no longer buying flagship phones.
Let us know how the story continues, and welcome to the community!