There's some simple things that could be done to improve the UI of the program even if you're not going to completely change it.
A good example is dialogs like this (I don't have BIAB 2010 but I'm assuming the dialog hasn't changed)
http://www.pgmusic.com/images/bb2007_screenshot4.gif

The layout is amateurish.
Now I know there's going to be a lot of long-term users that jump to the defence of BIAB but please understand this is an attempt to help pgmusic improve their product.
There's good reasons to have a layout that is well-aligned, it actually makes the dialog easier to read/use, this is a well established principle in professional software design. A simple analogy is the use of text alignment in newspapers and books which aids in readability.
The UI in BIAB has actually been used in computer software books as examples of how NOT to design dialogs, I think this is a sad state of affairs for pgmusic and what's worse is the small amount of time it would take to correct these sorts of things shows a lack of pride and professionalism at pgmusic.