If you can't hear a difference, does it matter? The price increase is a separate issue from the SINAD measurements. If the features justify the asking price compared to the competition for you personally, these measurements shouldn't change anything.
Two seperate issues... 1) in engineering terms there is a step down, 2) in audio listening threshold terms they are no different.... and 3) the X3800 gains additional functions (Auro, 4 independent subs)
It comes down to how does the individual value these - and how do you rank these alonside the retail price.
Auro and independent subs ranks highly in pragmatic terms ... listening threshold gives it a "get out of jail free" card with many people... does that make it worth the price of the previous X4700? - that's up to the individual buyer.
The move upmarket by D&M, means that the X3800 does NOT in fact replace the X3700 in market positioning, but instead is positioned where the X4700 was.... and so on up the range.
Can the X2800 fill the X3700's shoes? - can it go toe to toe with the Onkyo RZ50? Clearly marketing thinks so. Audio Nerds are likely to disagree!