My point of diminishing returns is softly defined by my mortgage payments

But seriously now, I am heavily invested into my headphone rig, but I recognize that I passed the point of diminishing returns and boarded the train to crazy town long ago. In a sense, I trained my ears to become more sensitive, which pulled my (financially allowable) point of diminishing returns higher and higher.
Depending where a person's ears are and what their financial situation is, the turning point must be flexible. My personal thoughts...
1) DACs his the point of diminishing returns the fastest. Stock motherboard stuff is generally pretty and at times is wildly audible just by playing frequency sweeps. A simple $50 external dac might be all a person will ever notice though. I'd say about $200 is the wall that most people will hit. There's perhaps anther plateau at about the $1k level, but having auditioned many dacs it becomes incredibly difficult to differentiate beyond there. I know people all spout about "source first", but I think above a certain point that doesn't hold anymore and money is better spent at the other end of the chain. In an overall sense, not counting when you're in crazytown, the dac should be the cheapest part of the system. Dacs should in theory all sound more alike than not.
2) I feel amps are in the middle ground. Personally I feel the Bryston 2B on the used market in the 400-500 dollar mark is one of the best price to performance amps you can get. Above that... I'd say you're wiggling into $3k amps (new) before. In terms of sonics, while I felt dacs should be more the same than not, I feel like amps have more flexibility to impart their sonic signatures.
3) On speakers/headphones/transducers, I firmly believe that the majority of your money should be spent here. The only exception here being if you're in crazytown and are perfectly settled on what you currently have and want to burn money on the rest of the chain. The transducers undeniably have the greatest impact on sound and money should be spent accordingly. Now with headphones, I'd say the first cutoff is just sub of $100, and after that your next plateau is around $300. Above that, there are your planar options right at $1k, and I honestly don't feel that any of the options above that are really worth it. I won't comment on speaker pricing at this time
4) power conditioners: fuzzy realm, but I always say just stick with a nice solid surge protector ($40-50) and don't go crazy unless you legitimately have power issues or want extra functionality like sequential powerups etc
5) cables: haha... I'll just say don't get the cheapest, get something with solid construction and proper shielding and geometry, maybe spend the extra few bucks if you want something that looks nice... but money should only go here if you've already spent good money on everything else. I honestly believe that the point of diminishing returns is... at most $20 a cable. I don't want to debate it beyond that.