The "value" curve may not be linear, but neither is our perception of pleasure. Many try to approach 2ch system building like they’re choosing car insurance. Not me. I get too excited by the nuances of different gear, and what unique sonic perspectives they provide, compounded by their complex interactions with other components.
A few of my most expensive purchases have busted the "pleasure" curve, thereby rendering arbitrary percentages and diminishing returns meaningless. They also tend to stick around a lot longer here than most budget "giant killer" components.