While I have spent hundreds of hours experimenting with interconnects on components. I have only swapped cheap, good, and better on my sub woofers… never heard a difference. I have read that most folks have not heard any or significant difference on using great ones. Having said that… I always used relatively inexpensive subwoofer interconnects. While I am not a fan of Blue Jeans… you probably will not hear an improvement by spending more. I would buy a second sub way before I upgraded the interconnect. Two subs extend the sound stage and have a big positive effect on the system.
Lots of little imperceptible things can add up if you are seriously trying to get the very most sound quality out of your system. I always am. So I would not spend a fortune, but would buy subwoofer interconnects after you get your second sub. Emphasis here is: I would.