While I hear you, being a new and one-off special that PowerColor worked and did their own R&D magic (not AMD) then I think for the exclusivity I might say at the $400 MSRP that the Vega 56 released at it has merit... If it has the perf/watt that makes it a good choice for the Mini ATX format/chassis. As long as it competes with GTX 1070's Single Fan Minis (aka: MSI, Gigabyte ITX ~$450) in that segment I see PowerColor has no reason to believe they should sell it for less than competition in the market.
200W for the 56 is possible in that form factor, but I doubt it'll be quiet at full blast.
What I CAN tell you is that a 290X at 280W and a Vega 64 at 300W with essentially identical coolers and you notice the average power consumption of the vega is much much lower.
In certain games the vega seems to not want to push, it does so much dynamic mumbo jumbo that I don't mind in most titles but the fastest pace fps games it does not always run full tilt for maximum fpsness.
nothing their driver software cannot fix
Having compared GTX1070TI (MSRP) and Vega56 near MSRP I must say the vega56 makes a really good choice, at those prices that is..
I have absolutely nothing bad to say about vega56, Vega64 ain't worth it (I paid GTX1070 price for mine, hence the reason why I have one) and I do not reccomend anyone buying a 64, go for the 56 if you're an amd fan, and consider the 56 if you consider 1070\1070ti.
If they can deliver up to 200W ~ in this form factor it's worth 450 $ easy, if they've gotten binned chips with lower voltages I say hell yes worth it.
90% of the Vega64 performance at 2/3rd of the power consumption