Whether you decide to quilt in the sashing is certainly a choice you need to make based on the overall quilt appearance when you lay it out fully. We are only seeing a portion of it. I think it might look like you missed some spaces if every other design element has quilting in it. I like to quilt just a small motif in sashings that complement the squares. Lay it out and look at it for a little while and see what you think.