I think pattern view, mixer etc. and spectrum/scope buttons should be moved to top next to transport control.
this would save some vertical space which would make sense these days when nearly all monitors are widescreen. If you have small screen 30px or so pixels wasted space makes a big difference, especially with trackers where things are moving downwards.
crude mockup for illustration purposes: https://www.dropbox.com/s/3hxxwj3003ngi03/renoisegui.png
I would also like to be able to see spectrum analyzer and DSPs when sample and plugin windows are active
also it would be great if the mixer was detachable just like sample editor and others.