I seriously doubt that changing interconnects or speaker cables will make much of an improvement
I seriously doubt that changing cabling would NOT make a significant difference!
Hi Jim: THE way to build a rig is to first settle on speakers that you enjoy, which you have now, and then optimize around them. The way in which you descrbe your sonic signature you are almost there right now. Yes absolutely do experiment with tweaks and cabling by all means. Shelving, footers, rack, roomtuning, interconnects, speaker cables, AC cords, AC line conditioning, dedicated AC circuit. There is SO much that you can do with what you already have. Cabling will absolutely improve your stage & image, and the Synergistics are a very good approach in my experience. I have a LOT of Synergistics in my rig.
I have to wonder about the Nordost though. I fooled around with those but they were thin and detailed in my rig. Still you never know: synergy is key to all things audio and the only way to find out what works well for your rig, your room, and your preferred sonic signature is to experiment. The cable that works great for my rig may be terrible for you, & vice versa, you just never know.
However if you want to experiment with speaker cabling I highly recommend trying MIT. Not their cheapest and not their best, just go with what's good-yet-affordable for you. I love the MH750 Magnum series although it's now dated.
Bear in mind that some cabling takes quite a long time to settle in, so don't think your first impressions are necessarily valid and give them some time before you change to something else yet again. 30 days is a good starting point in that regard. Have fun!