The code in those classes shouldn't even be complicated, most developers probably know how to write those functions, maybe in different ways but the result will be the same. I'm saying that because here's the thing - most developers buy these products to SAVE TIME because there exists something that we can modify and build upon.
People will still share the word "I used Opsive", especially if the source code is available to those that purchase this product. Now you will have the skilled developers talking about your products too, it won't make Opsive less valuable if they share the code in my opinion.
Right now how I see it, is you're catering for the middle tier market, perhaps those games that require less coding knowledge and even the most advanced functions of your product will be enough for the average game designer, but developers that wish to add extra bells and whistles this is not possible for them. I hope that makes sense