I read the crown faq but can't find an answer to this.
I completed my French tree a week or so ago, before my account got updated. I see it says the new crown system has new exercises but does it actually teach any new words? I'm trying to decide if there is any point to continuing with it since I had already completed it. If it has new vocabulary, I would. If it is just adding new ways to teach the old vocabulary I probably should look for something else. Does anyone know?
The French tree has been upgraded to Tree 3. It will have more skills and so on. There was a post about it not long ago by the French team.
It will have new vocabulary, more skills, and so on, so yes, you should continue.
Completing your tree does not mean you have seen every word offered in your French tree. I completed mine about a year ago and I'm still seeing words that Duo hasn't previously utilized. (And I'm still on the 2.0 French tree.)
As far as I can tell, the Crowns system itself doesn't impact the number of words offered in a language, though it may affect when it offers them, but the new French 3.0 course does include more words, though I really don't know how many. Even if they increased the number of words by 5 or 10%, that would be a huge increase.