What's your investment threshold?

I spent $650 on used Acoustic Zen Absolute ICs and another $650 on used Acoustic Zen Satori Shotgun speaker cables.  It sounds crazy but they are non-perishable items.  Many years from now electronics might fail and  speakers will get worn out, but cables will stay and even hold the market value.

I think most of us here have a governor on our wallets, bur we also probably prioritize differently. It seems as if owning the "top of the line" product is a high priority for you.
None of my components are "top of the line", but I do own a couple of cables that are "top of the line" . Though to be honest, when buying, I never really consider where what is in that company's hierarchy.

Mainly I am prompted by finding a good price on what I am looking for.
I am talking about real price, not list price, and buying used is not a problem for me.

The ARC Ref 5SE preamp that I just bought, I waited 2 years to find one at "my" price.
No, the 5SE is not top of the line, but it is a very fine preamp, IMHO.
So while I do not play the percentages game, or the top of the line game, I am fine with playing the waiting game. We all have our methods.

Bob Grost at Cerious Technologies makes very fine cables, great bang for the buck. I have not heard any of his Matrix line yet, but I'm sure that I will one day. Enjoy!

I chose all my other equipment first using good but relatively inexpensive used cables, then I upgraded cables to the point where I was happy with the synergy of the system as a whole -- spending as little as possible to achieve that.  Whatever percentage that is, it is.  And I imagine this varies greatly among all of us here, so I think it's not useful or even appropriate to assign a dollar amount or percentage to it (within reason of course -- nobody should spend 90% of their budget on wires, but maybe anything south of 50% should be fair game especially if power cables are included).  At this point it becomes about where my best incremental dollar is spent as per @twoleftears above. 

@elizabeth I also begrudgingly know power cables make a big difference but just don't want to spend big $$$ there (I know this is irrational as I too have spent a lot on interconnects and speaker cables, but there it is).  I'm going to make my own with some good bulk cable (i.e. Oyaide, Furutech, DH Labs, etc.) and good connectors (Wattgate, etc.) since it really does seem quite easy even for an idiot like me.  My guess is for about the same cost as the Pangeas and not much time and effort I can have PCs that rival $1000+ brand name models.  Anyway...

I have Audioquest WELs 8ft speaker wire and four power cords plus AQ Wind interconnect.

it is about 2x the retail of my speakers so it would appear my percentage lies around 35% of my system.

i didn’t plan it, just turned out that way