If you have a pair of speaker cables that are perhaps a bit lacking, is it better to spend the money upgrading them or try and use what you have in a different way?
The easiest, simplest answer is, of course, to spend the money and upgrade to a higher level. But, that isn't always practical.
I would guess that in about 50% of the cases I have worked with people on, separating the frequency duties by bi-wiring the speaker cables comes out on top.
One of the easiest experiments you can make is to roll your sleeves up on a Saturday afternoon and give bi-wiring a go (if your speakers have dual terminals).
Use your existing cables for the top end and a 12 gauge solid core length of Romex electrical wire (the same wiring that is inside your home's wall) for the bass. While this may not be the ultimate solution, it's an easy way to tell if the act of bi-wiring is worth exploring.
Sometimes, a little elbow grease and ingenuity can make a big difference in the performance of your system.
Worth a try.