I like the modern look of the layout, but I think I agree with you that a little more quilting would enhance it. If it were mine, I'd probably take cues from the print of each colored block and try to mimic that. For example, in the lefthand red block I would do a sort of "chicken wire" pattern. In the blue, little daisies. In the righthand red block, I'd do big x's. Or I might just fill in each space that seems too open with a wide serpentine stitch.