I think you can't mention the used cable scene enough…I doubt I would have bought a solid silver Audioquest sp/dif cable for my DAC at full price, but found one (years ago now) for cheap on Ebay. Same with a lot of other cables I own bought at 50% or more off the list price, and all in pristine condition.
What's your investment threshold?
This question only goes out to those like myself who enjoy the system gains running better cables bring. Non-believers can save their money and comments for another thread.
Do you impose on yourself a percentage range for cable spending relative to other components?
Speaking for myself, I do consider cables to be a component decision worthy of budget, but I seem to have stayed in the 10-30% range of what I've spent on other components. I can't see spending $1k for a cable on a $1k component for example. I have spent $1,500 for speaker cables for a $6k amp. That seems nearer the high end of my range but it still fits.
I realized I haven't planned this as a hard rule, but that's kind of how this has worked out for me over time. Anyone out there think a much higher percentage is justified? I won't argue because these improvements are worth all the enjoyment you can get, so more power to you.