If you search the board, hopefully you can after the upgrade, you will see many mentions of wire. This is a well discussed area of audio, with some suggesting expensive wires can and do sound better, and some suggesting that is just not true. You are correct when stating there is a limit to all equipment, but what you are trying to accomplish is not to limit what your equipment is capable of.
Speaker cables should be 12gauge in size, and for all discussions, can be purchased at your local Home Depot. You should think of cables as finishing touches on already excellent systems before purchasing expensive cables. They can "polish" excellent equipement, but will not greatly add to a systems sound.
Interconnects are slightly different, and you should buy decent quality brands.
You are correct in stating you can go overboard on cables. You need to achieve a balance. I would not use any "throw in" cables, as they are typically poor - unless you negotiate good cables as part of the deal.
