Synth1 is my favorite free software synthesizer to this date. There are a lot of preset banks available on the web. I had a look at the preset format and thought it would be easy to generate random presets if I could figure out how the values are stored. I decided to write a small Java application that can generate random presets. You can also visit the blog: BLOG.
Remember it is my current test program not a final and fully working version, and BEWARE it overwrites existing files in the specified destination folder. So think about selecting a free bank folder, or make a BACKUP.
At this time the program is very simple but is already quite modular due to the XML files you can modify. The next big step will be to clean the code and release it as open source, I think this small application has a lot of potential, it could generate random presets for many VSTs if the code source can be modified.
Try to hybridize presets that are close to each other, like two similar pads. This may generate many variations of those presets. Avoid hybridizing two very distinct presets, the results will be too experimental. Don't forget that you can save the generated presets in another bank. Also think about hybridizing the random presets themselves with other sounds or among themselves...
You can find some documentation inside the xml configuration files. I am not satisfied with the current modularity, but it is fairly easy to use right now. Also check the official documentation of Synth1.