I think youve got a good thing going now, I dont see this as a big money maker and making all your offerings public I think would generate you more money. If the genetics are there, people will buy them, if they arent, offering them to a exclusive group I dont think would help you much. I would keep selling your 'best stuff' via distributors and keep the limited editions as direct purchase only from your website. I think a big part of what people like about your deal is your openness and the obvious quality of your products. I could see you creating a 'testers club' or offering a discount or bonus to loyal/return customers, but charging extra for it I doubt would prove beneficial or you in the long run. You would have to do a cost benefit analysis to see what you come up with tho.
What I would do is select a few good growers to be 'testers', those who you know can produce not just nice plants, but also those who are willing to document and provide you detailed feedback and PICTURES of the plants they are growing. Keep this group small, maybe 5 to 10 individuals. Give those growers free seeds of genetics you would like tested, but dont have space/time to grow out yourself. Also provide them with a special shirt or some bonus for helping you out. Maybe make a restricted forum for them to discuss your products in private and provide feedback to you in a discrete manner. I wouldnt do this on a volunteer basis but select people who you are impressed with that have purchased your products in the past as normal customers. I think this would help you more in the long run. This would be more like an elite, private party type group that some people would obviously want to be in, but not something that you charge them to be in, it would have to be earned through demonstrated skill and sustained willingness to be of value to your company.