cables are they worth it?

I own a mid-fi system:
CEC TL51x $1500
Wadia 12 $500
VPI Scout $1200
Lyra Dorian $800
Rotel Pre and power $1000
Clearaudio basic $300
Impulse speakers $3000
Wireworld atlantis 5 $500

Total about $8300 my gut feeling tells me spending more then $200 per interconnect would be a waste of money. Soon my phono pre, pre and power will hopefully be replaced my an intergrated. Meaning I need 2 interconnects. Right now I own a Cardas Hexlink 5C and a Cardas Golden Five.
I asked an "expert" on what interconnects I should use and he recommened JPS Labs Superconductor 3 or Synergistic Research Tricon. Both cost around $800 each for 1 meter. Isn't that way overkill for my system?
The same for powercords would it be a waste to spend more then $50 on them, none of my power outlets are grounded.

Sure I would like to believe that expensive cables have a positive influence that is why I bought the Cardas some time ago. But I am really not sure if they are better teh a $50 wallmart cable.

Ps I live in the Netherlands.