Dave: Let me start with the big picture. Every marketing plan should be diversified. As such I counsel to go after the "right" agents, not top producers or rookies.
A good marketing plan will have elements of both. Top producers obviously have more business to refer. However, they are more likely to have existing relationships and many others beating down their doors. That is why it is important to deliver maximum value, i.e., help them increase their transactions. Lower producers and especially rookies have less business to refer, but are also less likely to have relationships.
That means you need to develop a value proposition from the start. And this does not include great rates and great service, because that is likely what their present loan officers are offering. If they deliver lousy service, these top producers would not be using them.
Who are the right agents? I really don't have time here to go over every aspect. However, here are a few. You want that agent to be ethical and loyal. Top producers become top producers because they make good business decisions. They are likely to have relationships because they know they need excellent service providers to be part of the team. Therefore, you want an agent who is going to be a team player. I think from this you can get the picture.