i asked this questions myself too. and i´ve done it. A8 feels much better than A6 and it´s more powerful.
i used the special rabate as A8 comes out, so that i have upgraded from A6 Com to A8 Com. I think this was the right decision. the only problem is that i have less time for it than i thought maybe in the holidays i can focus on it...

in your case i would ask myself: "will i finish my old projects?" if the answer is yes, buy A8 and do it. if you have doubt, don´t do it.