This should be a pretty workable solution.
Just create different directories within the Plugins/MilkDrop directory. Then, put any presets which suit dance in the "Dance" folder, any for rock in the "Rock" folder, and so on. If you want to use one preset for more than one type of music, then just copy & paste it in there.
Press "L" once you're in MD, then select the appropriate folder.
This way you can only have the presets which you like for that type of music, and you can set whether they run randomly within that folder using the "R" key. Is this what you meant?