Nitpick: It's not licensing for a language, it's licensing for a specific tool. Common Lisp itself is not proprietary (having a standard) and code can be portable across implementations.
To answer your question, I would say that the business model (of charging for licenses) is fine in principle, but developer tools is a very difficult business to be in.
Have you considered a student price, I like the idea of having CL on my phone (and eventually tablet) but the price is a bit step for me (and presumably other students) especially to get source code access.
To answer your question, I would say that the business model (of charging for licenses) is fine in principle, but developer tools is a very difficult business to be in.