DA:O yes, DA2 no; there isn't that many good things, even about the story, that'll require you to buy it. Just wait for DA3. Also, The Awakening DLC should be a good experience for DA:O, though again, it's nothing extremely special.
And as for the Witcher, a big hell yes! You will love the first game, and then totally flip out when you play the second. They're all worth every penny.