Yes, I do know about the premature attempt to contact NASA when the site was in Area 51 (sigh). However, now things are different, and it may be much more suitable (and safe :( ) for Public Affairs offices of NASA, ESA, and other space agencies to extend their outreach to one more space-related site.
A bit of background: This was a rumour that I've somehow missed, but I've asked in The Pod Bay and apparently (according to @JohnB, but I have no reasons to doubt his take), the proposal was made to the members of the NASA Spaceflight Forum, and not to NASA's PAOs directly:
JohnB in The Pod Bay:
that's actually kind of a rumor ^
it wasn't NASA, but a NASA fan forum or something
but they already said it was NASA in the official SE podcast so it's pretty much fact by now ;P
this was the forum: forum.nasaspaceflight.com
My take: By all means. If we're to gain reputation as a credible source, we'll need all the help from the already established names within the space science and industry. The sooner such names are involved with our efforts, the better, so they can also help with the fine-grained definition of Space Exploration, participate in the moderator elections process, and other Meta topics. On top of increasing the value of our Q&A.
So the question is, when is the best moment? Impatience could be seen as obnoxious, repeating same invitations over and over again, and only having a bit more to show for each time we try. And waiting too long can be seen as arrogance, as if we can do without them. I believe that now is the best time to start with invitations. We're out of private beta, and the community democratic processes has begun. We have something to show for, but obviously require input from the best of them. I think it's important to forward invitations ASAP, so they can partake in this process from the very beginning, and peer-review our already existing Q&A while it's not too overwhelming in numbers.
I think this is a great idea. I suspect the best thing to do would be to ask specific programs about questions relating to their program. IE, pass HiRISE questions to the HiRISE Team, Rosetta to the Rosetta, etc. Get them interested in a specific good question, and let them try to answer it better than us. Once they've answered a single question, I bet we'll suck alot of them in, including more than just the PO people. Twitter might be a good way to accomplish this.
Also, there's a site that I know is known to have lurkers around that have NASA connections, http://www.unmannedspaceflight.com . Check it out, you might get lucky.