Hi Vassillios,
Here is an often linked to web page that describes why you probably will not get any audible improvements with new wire unless the tips were totally wrecked or corroded or you were using too small a guage for the length of the run.
It also has a good chart to tell you if you really need to bother changing the guage of your other speaker wires because of distance. You will hopefully check your distances and find out that you are OK with what you have and can save the money for better speakers or other goodies.
Speaker Wire Explained 
