When building something you rely on your current knowledge and skills to create it. Yet I think it's important to keep starting from scratch every time you build something new.
Mental clarity
Start anew and the only issue you'll have is what you need to add, no bugs to fix, no rules to follow.
What was new gets old, fast
As new concepts and technologies become popular, many of the tools and pattern you used become obsolete and a new project shouldn't get held back by that.
Mistakes happens
You might think you've build something perfect, yet it breaks in a second in your new project. You should think carefully about what to keep and reuse to avoid issues in unexpected use cases that it wasn't meant to be built for, better keep things simple, generic and easily replaceable.
You'll get better
How do you learn something new? Probably by starting from the basics and working your way from there. When you look back at your first tries you notice the difference, this will happen with your projects too, a new project will always be the best one you'll make, because you learned what was right and what wrong from your previous ones.
Starting from scratch might be the best choice for you.
This is my personal opinion and surely won't apply to everything, especially on long running projects, but I'd like to know what you think.
Cheers! 😁