We've got some pretty important (to my mind) site-definition meta questions out there already, with more to come, but there hasn't been very much community participation on them to date. What can we do to get more of the community to come over here and help define how this site's going to work?
Don't forget the obvious — Simply start having the discussions.
Users will emulate what they see and a bustling meta with intriguing activities will encourage even further discussions.
But don't just copy/paste the overly broad, generic questions from that blog post and expect everyone to just jump in with definitive answers. Questions like "How are we going to promote this site?" sound more like a homework essay assignment rather than something that will inspire interesting content and get results. These activities have to remain interesting to the users. Instead, try coming up with interesting ideas of your own and ask specific questions that can rally everyone around small, incremental units of work.
The second way to keep folks engaged in meta is to treat every meta question like gold. If someone comes here with a problem, make sure their issue is tended to. If someone comes here with suggestions for the site, be sure to respond. There's nothing more disturbing than a user reaching out to their community to promote the site (or asking for help), only to be met with complete silence.
If you tag meta questions with featured, this will force the question to show up in the sidebar on the main site. (Only moderators can use that tag...)
Of course you're still limited in how many questions...
Judicious use of the system message (the blue banner up top) can also be helpful in pointing users to meta in general, or to a specific question.
And - patience, it's still new here ;)