I'm a huge fan of wire. However, for subwoofers, you'd be wasting your money. You already have decent hook-up wire. As for interconnects for subs -- it's hard to discern any differences, IMO. I'll admit that I haven't spent several hundreds of dollars or more on a subwoofer cables trying to find out, but I'm guessing you'll need to spend around half the price of what you paid for your subs to hear a substantial difference. Obviously, that's not a good idea. For example, Synergistic Research is supposed to make a great subwoofer cable, but pricing is quite steep, especially if you need two of them, and fairly long runs, as well.
OK, that bring us to the power cord. Absolutely!! Get the best PCs you can afford for the amps. There are a zillion good power cords on the market, so getting recommendations is probably not helpful. To narrow down your options, I would suggest supporting one of the seller participants on this forum who design and sell great cables at reasonable prices.
The most significant improvement I received with my OB servo sub was when I got an UberBuss. I was shocked that the bass went to a completely different level -- cleaner and much more authoritative.