I think it'a also important to take into account that many brands/models of cables will lose little or no value over a few years, and can either be sold or grow with your system...Kimber 8TC or 12TC are a great example...
How good does my system have to be to realize an improvement with cables?
I've heard the difference power cables and interconnect cables in a highly resolving system so that's not the question. $200 for cables on a $500 DAC doesn't make sense to me. Wouldn't that $200 be better spent on a better component? At what point is an expensive cable the best choice? Spending $500 on a $15,000 DAC does make sense as the transparency and resolution of the component could be better realized with a better signal / power source.
My question is what's the percentage of the overall component's cost should be the cabling and at what point should it even be considered?
Or put a different way How would you know if your cables are your weakest link?