I absolutely agree with what Lisa and Kirsten say - it's a GREAT resource and a great challenge, especially if you are starting out writing PBs. I did it for 3 years a few years ago.
A couple of things to consider:
I don't think you can get GOLD right away. And the GOLD level is awesome with the submitting to agents option, but don't spend the $ on GOLD assuming you'll get an agent. Yes, some people do. But obviously, it still comes down to the writing, so if the agents don't connect to what you are writing, you might not hear back from them. (I know that is probably an obvious statement, but I do think some people go in with rainbow blinders on and get frustrated if they don't get responses from the agents.)
You'll get out what you put in. It's been a few years since I was there, but there was a great forum where you can network with other writers, get critiques on your first hundred words, find critique groups, and ask any question or find any answer you want. And I found the motivation to click that checkbox every month that I wrote a draft very helpful. At the time I was in, it was a Rafflecoptor and each month you had a chance to win some sort of prize. I don't know if that is the case anymore.
The three years I was a part of it, I LOVED it! Why am I no longer a part of it? After a point, when I no longer felt like a "beginner" but I wanted to take some more classes or attend retreats, I decided I could use the $ I spent on membership in other ways to improve my craft. But as Kirsten noted, I did, and still do miss the 12x12 community. And it was certainly $ well spent when I was in it. Did I get my agent through it? NO. But as Lisa said, I wouldn't be the writer I am today if 12x12 didn't help me at the point in my writing career that I needed it!
Hope that helps!