For the record.....I'm mostly neutral on the discussion. I've had to make changes to my converters over time, and as my income increased, the cost of my converters has increased too. I don't have Lynx or Apogee, but a pair of RME converters. What I have noticed is that the more expensive converters
generally offer more channels of AD/DA, options and are easily expandable to add more and more channels. For example, I could add another 16 channels and record all 32 simultaneously while holding up and keeping latency down.
For comparison, all I can do is listen to my older recording versus my newer ones. Honestly, there's things about the older recordings that I like better, and there are things that I like better on the new gear. I think that the more layered and multi-channeled the work, the more noticeable the differences are. Most of the stuff I recorded earlier on was simpler, and now there is more going into the recordings (literally), thus I like the RMEs better on work that has larger track count.
Last, don't forget that Apogee, Lynx, etc. are really designed to be pro-grade converters that live between large consoles and the DAW with the ability to record 48+ analog sources at once, powered on and in use 24 x 7. Most of us don't have these requirements, thus we don't need to spend the bucks on them.
It's no different than the exact same discussions about cameras. Does an artist need a $5000 DSLR body? No. Does a pro that will lug it around all the time, drop it, and depend on it for her/his living? It's not because it takes that much better pictures, but because it gives a professional the tools they need to make their living without cause for concern. The camera built into an iPhone can take a picture of the same quality as a $5k DSLR (for the most part) and certainly when in the hands of a regular person. Thus, the $5K DSLR is not intended for me, but the manufacturer wouldn't mind one bit if I could afford one.