Lucas: improving our relationship with potential new contributors is indeed most important. I buy your analysis on the barriers. Let me comment on the various barriers:

• psychological (self-esteem? unclear initial steps? project is too big?): from what I have seen (on mailing lists, but also at some events), a lot of people just think GNOME is too big for them. And most of the time, they don't know how to start. GNOME Love is a good way to destroy this myth. But to make this effort even more effective, I think we need to spread the word. This is where local groups are important: there are a lot of events where GNOME is represented and if at all those events, local groups can talk about the GNOME Love and show a concrete example on how to contribute, then this is a big win.
• social (community is not receptive? contributions not being considered?): we have a first problem here, since it's hard for a maintainer to find time to contribute and to review contributions (be it code or ideas). It just takes too much time... I'm interested in a magical recipe to help with this.
• technical (bad platform docs? gobject is too complicated? don't know C programming?): it seems the most difficult part is to get a first build of GNOME. jhbuild is great, but I'm sure a lot of people would love to download a simple script that would do all the jhbuild configuration for them. Might be a nice python project :-) The waited-by-everyone library.gnome.org will also help here, I believe. I don't know what's its status, though.
• cultural (don't speak english? doesn't have local group to share knowledge/information?): local groups are really important since they can spread the word. We should definitely help them as much as possible so they don't have to do a lot of work to start. Go, GNOME-BR, go! :-)

Quim: don't you have a global vision of the GNOME websites and the online channels we are using? When I read this, I think you have the vision :-) You can be the one. I agree that it's kind of difficult to find the right place to discuss this since there are a lot of people involved, but I would think gnome-web-list is the right place. Just announce it everywhere, like on the Planet. Try this:

Are you interested in the GNOME websites? If so, subscribe to gnome-web-list!

:-)