But not critical.

This guy is worried about the difficulty of the install. R/L for wire in your average car is sufficient.

 

If it's a noticable difference then I may as well just grab new speaker wire. Is it worth it in your opinion?

 

There's a neat calculator on BCAE that will tell you whether you'll hear a difference or not.

If you're running ~75watts to those, and if your car speaker wire is at least 16ga (probably is), then you won't hear the difference.