You can reap some big cable improvements by unplugging them, and then plugging them back in again.
This cleans off some of the oxide from the connections. Some people choose to unplug them, drive a long distance, spand a lot of money on new ones and plug those in, but the effect and the cure is the same: just unplug them and plug them in again.
Then you can spend your time and money on something that actually will make a difference, the things that make the most difference are in this order:
3. DAC/CD player
Remember when you audition speakers make sure they are driven by a decent class A amp or a tube amp, as some scratchy shrieking class B transistor with oodles of feedback to wreck your transients will change the sound of many speakers quite dramatically.
Oh and use copper for cables. Just good old plain copper. It's the best conductor (some types better than silver) and is readily available in good sensible cables at reasonable prices. Oh and about the DAC - pro-audio DACs are in my view far superior in quality and value for money but many CDs will not sound good through them as you can hear the CD clipping - most CD/home DACs have much better clipping - the average clipping rate on many CDs now is over 200Hz.
ETA: if you are worried about RFI pickup in cables, buy some clip-on Ferrite Cores from Rapid for about £2 each and cip them over the speaker cable near the amplifer. In some cases (where RFI is a problem and you run a deep feedback amp) this will improve the sound.