Those numbers are for mining ETH only though. I'm not sure what kind of load or voltage it takes to dual mine, but the last time I tried it (way back when Claymore first implemented it for DCR only) it was way too high. With ETH only the cards are running @ 850 - 925mV @ 1220MHz on the core.
Yes, the power usage isn't as good if you dual mine... But if you were mining DCR and holding it back then... It's worth $34 or so now, instead of $9.
DCR is a great coin with a lot of potential. I still have "some" rigs dual mining DCR.
Most people dual mine and do whatever is profitable at that moment. They don't analyze the potential for the coin long term.
I see both sides of the coin (see what I did there?) but in my own experience going for the long term has proven to be more valuable.
I agree with you on regarding Decred, I think it will have a jump to going near current Monero prices in the not too long future.