If a site has changed significantly, then it is reasonable to resuggest it--regardless of whether it's been reviewed or not.
If it has been reviewed, the new content might mean it's listable now.
If it hasn't been reviewed, then your new suggested description (mentioning the new content) will help the editor, whenever it IS reviewed.
Six months after the last suggestion, and, say, three months after the first significant addition of content[*], would certainly be a reasonable time to resuggest.
(Why do I throw in the "three months after significant addition of content?" Think about it. Suppose you suggest the site in january. I review it in july (you don't know that!) You add content in august (I don't know that!), and IMMEDIATELY resuggest. I happen to see the site, and say, "I just reviewed that last month." If there's nothing in the description that strongly suggests a re-review is called for, I might just delete that suggestion "as a duplicate."
BUT...if you add content in August and don't resuggest till winter, I'd be more likely to say "I haven't looked at this in awhile, let's see if anything has been added."
This isn't an ODP rule or anything against suggesting immediately after the content is added. It's just my personal recommendation, to avoid an unlikely but potential problem.)