Comparing the (Uncapped) Sony A306 & NW-WM1AM2 | Law of diminishing returns in audio

Sony A306 £349
Sony NW-WM1AM2 £1300

"Which one sounds better?"
The NW-WM1AM2. Larger stereo image/soundstage/field of sound, etc and a firmer bass.

How much better? What is the scale/level of improvement in sound? Maybe 5%, at most.
Unfortunately BOTH devices have a pretty unacceptable level noise floor (hiss with IEMs).

Despite costing more than 4x more the Sony NW-WM1AM2 only sounds marginally better than the Sony A306. The difference is not "night and day" but a bit better.

The law of diminishing returns is certainly the case with audio. Spending 2/3/4/5/10x more will not get you that level of improvement. The gains will only be marginal/fractional, if there are any gains at all.

IEMs/frame of reference:
Thieaudio Prestige Ltd £1149
Elise Audio X Symphonium Helios SE £1099
Campfire Audio Dorado 2020 £1099
Thieaudio Monarch Mk3 £899
Thieaudio Monarch Mk2 £800
Sennheiser IE600 £599
Thieaudio Hype 4 £349
Fiio FD5 £289
Penon Serial £289
Ziigaat Doscinco £254
Ziigaat Cincotres £254
Fiio FH3 £120
Fiio JD7 £89
KZ ZS10 Pro £45

DAPs/frame of reference:
Hiby R6 Pro II £600
Hiby R5 Gen II £450
Hiby R3 Gen II £179
Hiby M300 £179
Hiby R6 £1400
Sony A55 £200
Sony A306 £329
Sony NW-WM1AM2 £1300

My Ebay: https://www.ebay.co.uk/usr/lure-1286

Ziigaat Cincotres for sale £180 (UK only)