Dear Sean Owen,
I have read the old posts introducing BS+, I understand the motivation and how it helps improving BS and the Zxing project. I am pretty happy with BS right now (except for the lack of aztec code support) and I am not specially motivated to buy BS+.
I am primarily interested in supporting free software (as in freedom) so I prefer donating to a free software project better than buying a proprietary application (even if it contributes to the project somehow). I would like you to consider to open-source BS+ and move it into a supporting version of BS. It will have a price. You would get:
BS: the same general functionality we are used to.
BS+: newer features, more frequent updates, a more direct way to support free software.
Of course, new features in BS+ would have to be moved to BS in a timely manner. This would attract more BS users, hopefully make more BS+ costumers and increase the profits as a business.
I would happily buy BS+ right now in these conditions (as I have just bought a support donation to Cool Reader ).
Under these conditions, you may also consider GPL if you want to prevent close-source derivatives.