What are sensible cable costs relative to the total system cost?

"Since making a spread sheet with my audio system prices, I have been thinking(shocked) about my total investment in cables. My total system retails at $67,000 (Digital and analog front ends included). I purchased all of it here on Audiogon so my investment is about 50%. Of that I have about 10% invested in interconnects and cables and another 10% in Power Cables (Shunyata Hydra included). That's $13,000 worth of wire. 

I'm starting to question whether it might be more effective to put some of this budget into acitve components. It would take forever to listen to all possible combinations, but would like to hear others experiences with relatively high end systems and cable selection. It would seem to me that the point of diminishing returns would be reached sooner with cables than with speakers and amps. Do most of you follow the 10% "rule" for cabling? How do PCs fit into this rule? Are there any super bargain cables capable of keeping up with highly resolving electronics"