If none of those apply, then some signs that a site might be listable:
(1) You describe a site as "the only site that has (some kind of information.)"
(2) You think of other informational sites as "collaborators"; or, before you even started the site, you thought of real people working in real buildings to provide real goods and services for surfers, as your competitors.
(3) You don't care what the ODP does with your site: it's an expression of yourself--your knowledge and skills and experience and professional aspirations, and that is enough justification for any site! You'd like like-minded people, or prospective customers, to know about your site, but if you need business advertising, you know how and where to purchase it.
(4) You are the guru of your niche: the person other professionals in the niche naturally gravitate to for help, when they're out of their depth. Your site can't help but be in that niche, because that's where your experience is.
(5) Your "industry" has nothing to do with the web; if the web didn't exist, you'd still be the same expert (enthusiast or professional) that you are now. The web is just a tool you use to express your pre-existing skills and tastes.
(6) You build your own site to your own standards, and you expect everyone else (including the ODP contributors) to build their own sites to their standards. But you can learn something from someone who knows something you don't, even if you think you know something they don't also.
(7) Before you began preparing your information for online publication, you spent hours researching the web to make sure it hadn't been done before.