Brent,
Without knowing some more details, its tough to give you a solid answer, however I would suggest focusing on hard benefits and differentiation. Measurable financial benefits, not just soft benefits. Remember, agencies work for their clients and even if they fall in love with your concept, if you can't help them sell it to their clients with measurable data, case studies, results, etc they will love it and still not bring you any business.
Another thought....why are you targeting agencies vs. the clients themselves? Especially in early stages, before you have solid results to show, it is often easier to approach a budget owner directly. Then, after you have a solid case study, you can scale it efficiently by selling in to agencies.
Best of luck!!!
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