Thanks for posting a pic of your test Chris! That looks just as I envisioned it would, gives subtle texture without drawing attention away from the fabrics and pieced design. Are you pleased with it? I think your variegated thread looks good on it and does not detract from the piecing at all. So I would definitely rethink my suggestions of a very fine, neutral thread. The variegated gives little additional shots of color here and there and I like it, especially on the dark blue batik 1/4 circle on the lower right.
Matchstick quilting definitely will flatten a piece out but in the case of a wall hanging I prefer flat and even stiff! So I won't hesitate to lay a lot of thread down on a wall hanging.