Vocabulary knowledge should decay faster/ easier when translated wrong
As far as I'm concerned, the strength displayed behind my learned vocabulary does in no way reflect how well I feel I know them by heart. There are words I used once or twice, when they pop up the third time a day later I can't remember them, so I peek or get them wrong, but they stay at full strength. They should go down a notch or even two whenever I get them wrong and then turn up more often in my practice so I can actually repeat and learn them.
According to learning theory, new words should be repeted after a few hours, then (if correctly remembered) a day later, then again after another day, then maybe five. Then two weeks, four weeks. Whenever you get them wrong or have to peek, they should go back into a lower repeating shedule. There are surely people here on duolingo who prefer all their vocabulary staying golden at all times, but I prefer to learn the language first. Once I successfully have kept a word in my mind for a month, I don't have to repeat it that often anyway and it will stay golden.
Anyway I feel like I deliberately progress through the tree much slower than I could, out of fear to accumulate a huge vokabulary that I in no way would have learned. If you don't want to slow down the "goldening" of skills and vocables to not discourage more casual learners, I would suggest an optional setting to set in my profile which lets me progress slower and makes it harder to reach golden vocables.
The learning theory you're describing is called spaced repetition.
Anyway, I've fallen prey to this to in a slightly different way. I tested out of adverbs without finishing all the lessons, because I was confident on the material I had studied so far. I passed the test, and DuoLingo said I had learned 80 words! Not only had I 'learned' words I'd never seen, they were at full strength! Without the strength of these words decaying as I peek, I'll never see them enough to get very familiar with them.