I participated last year and signed up again this year, and love the motivation and support from all the 12 x 12 participants. But this is only the second year the challenge is running...and it didn't cost anything last year, so there's no way to tell how much the higher levels will help.
There's definitely a lot more offered this year--like an agent or editor you can submit to each month (and bypass the slush pile--plus I believe two of the ones listed aren't open to subs unless you see them at a conference, have a referral, or are a Gold 12 x 12 member). One of my favorite parts of being a Gold member so far is the query critique session, where Emma Walton Hamilton gave incredible feedback on about 40 queries.
I've been pretty busy revising my MGs and keeping up with my critique groups, but if you have the time to put into critiques, I've been impressed with what I've seen in the private forum for the first 250 words of a PB, queries, and blurbs. I definitely plan to participate in the critique section when I have more time!