The Druid combo is one of the more likely things to get nerfed. Whenever they do that, they give a full 100% refund for cards crafted, so there isn't much risk in crafting Force of Nature.
Ancient of Lore will almost certainly still be a great card after the next expansion hits, so I think that's a safe craft choice as well.
That being said, I always tell people to wait at this point since I'm sure there will be a lot of really good cards coming out. If you really want to craft those cards, the ones you mentioned are safe choices as I have outlined above.
I disagree. Ancient of Lore is pretty safe. If nerfed, you can dust it for full value. If not nerfed, it will come good in quite any druid deck. Contrariwise, Force of Nature is risky. They may nerf Wild Roar, and this way make Force of Nature unuseful without giving you full dust if you want to get rid of it.
I crafted the missing pieces, played around 26 ranked games(my first games with druid actually), so far I'm 20-6, now I see how OP this is... I feel dirty.. but happy lol. But I'm feeling I need much more practice.