As I read the ODP Social Contract, we promise to review a submitted site--once. Any subsequent reviews are because the editor thinks it might be a good idea, not because there's any ethical or social obligation to.
It is reasonable to expect an editor to NOT review a site that has been suggested and recently reviewed and found lacking unique content.
Normally, I'd expect an editor to re-review a site that HASN'T been reviewed at all recently, and HASN'T been reviewed much more than two or three times--unless there are other issues.
Basically, website owners have one or two free shots--after that, it's reasonable to expect that you're building a reputation, and you'll have to live with it.
Given that, what would the recommendation be?
(1) If you realize you had suggested a site without significant unique content, and you recognize that you now DO have "significant unique content", then do two things:
-- a. Mention the added content in your proposed description in brackets as a note to the editor: [added complete Galactic Encyclopedia, 2130 edition (or whatever)]
-- b. wait at least 6 months after the addition before resubmitting it.
That way, no matter how it works out, the site will not have been "recently reviewed with inadequate content", and the editor will know there's something new if it was "previously reviewed with inadequate content."
(2) If you've already been through step (1) more than once, and you've decided your prior judgment wasn't right -- then stop. The pattern is, you're not good enough at recognizing unique content to be a help to the ODP. Let someone else with consistent, better judgment (i.e. an editor) find and suggest the site. And you'll avoid building the kind of reputation nobody would want.
CAVEAT: I should mention that this is my advice, not official policy. It's based on my experience of how editors really work, and it's designed to make sure you don't harm yourself by deliberate actions, and that you're not harmed by unfortunate synchronicities between your actions and editor's actions.
I can't guarantee that you WILL be harmed if you DON'T follow this advice, and (as always) I can't promise that editors don't make mistakes, because we do. (We've fixed millions of each others' mistakes already.) I think I can guarantee you won't get a reputation as a spammer if you work this way.