This very helpful user pointed out to me exactly what parts of the FAQs made him think that submitting a suggestion to suggestions would get him an invite code. I think that should be changed.
FAQ 103: How many invite codes can I generate? How can I get more? states:
In addition to invite codes gained by virtue of account type, you can also earn invite codes by contributing to LiveJournal. To learn about the different ways you can contribute to LiveJournal, see http://www.livejournal.com/support/faqbrowse.bml?faqid=57.To an unsuspecting visitor, this clearly implies that any way of contribution that is listed in that FAQ will get you an invite code. Then, of course, FAQ 57: How can I help? lists (as one of those ways) making a suggestion.
I don't have any specific idea of how exactly to change this, but that's no surprise at this late hour. Please discuss! ;-)