I feel your pain! I just finished "un-quilting" about half of a throw I'm making for my MIL because I was very unhappy with the quilting. It's the largest quilt I've done and also one on which the quilting really shows. The quilting thread blended much better on all the others I've done. Also, I did a bunch of spirals, which was a new-to-me FMQ stitch.
I didn't worry about previous marks or needle holes because I believe those will be taken care of when I give it a final washing.
In the end I am glad I did all that stitch ripping because now that I'm quilting it again it's looking a little better. I had given it to her at Christmas (more like shown it to her because it wasn't finished). It's made from my DFIL's shirts (he died three years ago last Thursday). Mom didn't care if the quilting wasn't perfect (she said everyone has to practice) because the quilt itself means a lot to her. Hope to have it all done for Mother's Day.
Good luck with your fixing. I'm sure it will be worth it once it's done.