Rhonda, in my opinion you should always buy the best fabric you can afford - emphasis on what you can afford! Fabric prices are high and unfortunately, our budgets are low! Nonetheless, being picky is always a good thing.
Like you, I haunt sales. I have a large stash, probably because I like fabric a lot and quilting is my excuse to buy it. Most of my fabric is from sales, and I buy because I like it. Here and there I buy a fabric because I HAVE TO HAVE IT! The 'have to have it' fabrics are very difficult for me to use because if I use it, I won't have it anymore.