From the question, it's not clear who the customer is. It mentions 1. Event Planners, 2. Top Venues, and 3. "general consumers/mainstream". Each of these has different goals and needs and probably will buy a different product if they buy a product in this space at all. So my take is that this may be less a hurdle with regard to marking marketing and more of one around product.

Because of the way money flows in the industry, it may be better to focus on meeting the needs of venues because they will collect money directly from the transaction and can dictate that your service be used for bookings. Event planners on the other hand are paid outside the booking transaction that you're interested in and they have venue options that are unlikely to appear in your marketplace, e.g. churches, parks, etc.

Good luck.