Worth upgrading my cables?

I’d focus on room acoustics and speaker placement first. 

As far as cables go, I’m familiar with the 4S11 speaker cables since I own and use a pair of these. They’re nice and warm sounding. Not the latest word in transparency and soundstage but are not bad by any means. You can do better. After the speaker cables I would tackle the power cords. Synergy is key. Either borrow from The Cable Company or buy used or get new cables from a dealer with a proper return policy. Auditioning in your system is a must. 

You would absolutely benefit from changing your speaker cables to Morrow, but I would at least go to the SP-4's. I had SP-6'S and sold them because I needed a longer run. I replaced them with Canare 4S11's and everything completely collapsed! Presence, soundstage, details and it sounded like the speakers were shouting music at me instead of placing music in the room. Now I'm completely satisfied with Morrow (SP-7's) speaker cables back in my system. But like I said, SP-4'S is the lowest I would go in the lineup, as I have gone through this before. Throughout the years I have had SP-4'S, SP-6'S and now SP-7'S. My interconnects are Dig-4 and MA-7's. And I promise you that even after months of use, they keep getting better! For power cables, I have all hospital grade 14awg from Amazon and I'm happy with them. The only cable that I will eventually replace is the Dig-4, and I'm going to replace it with the Acoustic Zen MC-2 since I hear so many success stories about it. Have a great day and enjoy the music! ✌️

My suggestioin is to get get your hands on as many cables types in as many price points as you can "reasonably" get your hands on. This would include cables above your "comfort zone" if they can be returned. Expanding the size of your "toy box" makes things a lot more fun, and you’ll get to experience things outside of the scope of "highly recommended" products. I’m going to predict that you’ll find improvements in areas where you least expect it. To me, this is often the most rewarding aspect of upgrades. The price of admission may be less than you budgeted, or a whole lot more. Your internal calculator of value vs performance is the final, and most important, variable.

I would also include upgrading your wall outlets. IMHO power delivery is often the most underappreciated aspect of system performance.

One more thing. I’d consider putting $10 worth of Dynamat on those Heresy horns.

Assuming that you have solved, power distribution, speaker positioning, turntable/ cartridge alignment, components support, any room treatment (if needed), then better cables, no matter if silver or copper, will definitely have a positive effect. Everything matters for achieving a good sound not just cables. You can find a good and reputable dealer and borrow complete sets to try out, and save money in the long run. I have a sweet spot for cables that use means of better conductor manufacturing process so that leaves out for me the majority of the pro called cables. In an era of Triple C, Ducc or even OCC (all of them having advanced methods of manufacturing), the ones using OFC are lacking. But good sound of a cable is not only determined by its conductor but by its overall construction, the materials used, the geometry and the connecting component.

After trying out and experimenting you can only decide what is good for your system.