Sure is handy not to have to patch together volumes controls, clippers, 'External' primitives every time you want to just try a little experiment - and I particularly like you idea of making schematics a bit more 'transferable', and the little 'signal generator' toolbox.
Here's a little screenie of the little blocks I use at the moment...
...they don't do much besides quckly setting all my preferred soundcard settings, a quick way to turn them on/off and change the volume, and some pretty labels to remind me what my hardware i/o is connected to.
There could be some useful stuff to be ripped out of my Exe I/O Modules
schematic. They're designed for embedding into an .exe export, to edit, store and recall the soundcard settings (and any other data) into a .ini file. It would need some adapting, but the method has the advantage that all parameters are stored and recalled by name - an easily readable format with a published list of variables and ranges then makes it easy to deal with adding new features, or people who prefer to use their own skins or a slimmed down feature set.
Couple of other suggestions...
Some basic metering (perhaps just 'signal present' and ''clip') is always useful - I've lost track of the number of times thought a schematic was broken, only to find that I forgot to plug the mic lead in!
A quick on/off toggle with shortcut key - the one thing I miss from SynthEdit! Could also send 'All Notes Off' to MIDI drivers before turning all the drivers off.