Was it Hobbs 80/20 batting? If so, you definitely do not need to add additional quilting. Hobbs 80/20 can be quilted up to 2" apart and will still hold together very well.
I personally don't do SID anymore. I have a Bernina, a walking foot for it, and a foot with the black "plow" that rides in the ditch, but I still don't like to do SID. It makes me nervous because I see all the little deviations in the line and *hate* that. This makes me tense while I stitch, and my eyes practically fall out of my head trying to watch where each stitch is going to fall. Nowadays when I want to do SID on a quilt, I use a serpentine stitch instead. With the serpentine I can depress the foot pedal to max and casually feed the quilt to the machine; small deviations in the stitching are unnoticeable. Plus I like the soft look the serpentine stitch gives to the quilt. (However, I would not use serpentine if I were planning to FMQ.)
The only reason to do SID before doing FMQ is as an additional basting tool. Once you do the SID around the blocks, the layers are not going to shift on you while you do FMQ. A much easier way to achieve similar stability is to (1) heavily starch your backing fabric before layering, (2) spray starch your top before layering, and (3) spray baste with 505. Starch stabilizes fabrics so they don't distort while you sew. Spray basting secures the quilt layers together at all points, making shifting much less likely. (Thread basting and pin basting, in contrast, secure the layers only at the points where they intersect all three layers -- usually about a fist's distance apart.)
So, my advice at this point is simply to perfect your FMQ. If I had to choose between the two feet for straight line quilting, I would choose the walking foot because it is so much more versatile -- will work for cross-hatch quilting, piecing, and sewing on bindings. The "plow" foot is limited to SID.