Anyone add headers after, wonder why they waited?

My plan for my 318 build is to keep the Dakota 360 manifolds for my ebody, saving about $700, but I was wondering if anyone added good quality headers after building and running similar log style for a while, and how they felt about it. Was it a huge improvement? We can talk numbers all day, but I am not sure I have ever felt a 20-30 hp gain before, so I am looking for descriptive words. Was it great, wondering why you waited, or closer to modest improvement that you hardly benefit from on the street.

Thanks