I think we should use fabric that bring us JOY - this comes from not only the colour, hue and pattern but also the cost.
For some not using the best fabric when they spend so much time on a quilt would not give them joy. For others cutting up or risking messing up expensive fabric would reduce them to tears and they would not have any joy. Each to their own
At the end - do you love your quilt - thats what matters not what it cost to make.
But I do think you should buy the fabric that makes your heart sing - as long as it doesn't make your bank manager cry.