I will get something to add to the scraps, like a background. I think it helps unify the project.

I always start with what I have, and add solids for relief , borders, or binding ....which I often have to buy. I buy charm packs for $0.01 or $1.99 at msqc daily deals and often cut them into 2 1/2" charms for swapping and adding to my scrap collection. You are not alone.

I do many scrap quilts. I have two rules I live by. 1. Use everything you have. 2. If a fabric looks good with it's neighbor (the fabric it is next to) then it will look good in the neighborhood (the quilt). I've never been disappointed in my choices even though I've used some weird and/or ugly fabrics. There are always enough bright and beautiful fabrics to make up for the less fortunate pieces. Waste not want not and all that stuff. :)

I have several "scrappy" quilts model, quilts I like to make with about 50% of scraps. But I always need to add some "new" fabric to get a coherent look (either from my stash or from the fabric store). It`s ok for me.

I've bought scrap bags from Etsy sellers, but never bought new yardage to make scraps out of!

I did have to add a color (orange) when making a Bonnie Hunter mystery quilt (Celtic Solstice) as I just didn't have any then. And I've purchased some for background to calm down the chaos of my scraps!

I have because I don't have a stash and not enough scraps from other projects to make a quilt.

I sometimes buy scraps for a scrappy quilt. I get bored with my same old fabrics. It also gets me going when I lose my quilting mojo.

One of my first quilts was scrappy. I had to buy all of the fabric. It was the ugliest thing you never wanted to see. Not real proud of that one.
I am just now starting a quilt I am calling scrappy. I know I do not have enough stash to do it, so once I know what I have, I can go get the rest I need to finish.
Do what seems right to you. But have fun with it.

Sometimes when I make a scrappy quilt, I need to buy the border or background fabric. I spend too much time making the quilt to use a border or background that is not just right for the quilt. I figure using 80% scraps is still better than buying all new fabric.