Yeah, for 13CH Atmos 7.1.6, I think the only other components in similar price range is the $4,500 AV8805 (as you stated),the $4,000 Monoprice HTP-1, and the ATI ATP-16 (? Price).
So the $4K X8500 (which already has 13CH amps) is a good value from the immediate financial point of view.
Regarding "future value", only time will tell. If it lasts 10 years or more, then I say it's a good value. If the 13Ch amp + other circuits SOMEHOW make it even less reliable (with all those electronics horseshoed inside that chassis),then it will not be a good value.
So hopefully it will be reliable for at least 10 years.
If the $4K Monoprice HTP-1 pre-pro lasts 20 years and the $4K X8500 only lasts 8 years, then I'd say the Monoprice HTP-1 is a better value. Only time will tell.