Re: yes
"if you post a good concept it is very likely it will be stolen or, if stolen is too harsh a word, 'commandeered'. very much so"
Most people who become writers do so because they want to tell their own stories. While it's certainly possible someone might see your idea and decide to run with it, a.) it's not, despite what kojled says, "very likely", and b.) even if it happened, it's even less likely that the swiped idea will make it into the hands of a producer in script form.
I don't post ideas because no one can tell me whether they're good or not until I've developed them into stories. And even then, no one else will really know how I'm going to transfer that story into script form. But aside from that, I trust my own instincts. If I think the idea is a winner, I'll write it.
I don't know if there are really any new ideas or not. Probably nothing anyone will be interested in, just like there probably aren't any new ingredients for cooking. You can make new recipes, though, for those old ingredients. That's the key.
If you want feedback on your ideas, go ahead and post. Some people will tell you to stop asking other writers to do your work for you. Others will give you endless suggestions on how to mold your concept (which will probably be nowhere close to what you had in mind). Knowing that's the likely response, what you do from here on out is up to you.