Unfortunately, in my opinion, Quinoa is not Paleo.
Why is it not Paleo?
Quinoa is not a grain and it has no Gluten but the husk contains toxins known as Saponins that can give you much the same effects of eating grain. It increases gut permeability and leads to all sorts of issues.
In addition it also boasts a Glycemic index of 53, due to its high carbohydrate content along with a very high Omega 6 ratio.
What is a substitute for Quinoa?
There is no one to one substitute for Quinoa. It contains a fair amount of Carbs as well as Protein and no other Paleo food can replicate that. Get additional carbs from Sweet Potatoes and increase your meat content for more protein.