I just created a quick couple of VIs to test this and while I can watch my boolean button being pressed by the other VI, the Value Changed case was never activated (unless I clicked on the button directly and not through the other VI). It looks like it might be back to polling for changes or use the LV7.0 user defined event (a suggestion from one of my co-workers).
I didn't expect Mouse Up and Mouse Down to work, but it would have been nice if Value Changed had worked. Perhaps in the next version?
For interest's sake I have included my little test VIs here - they're simple enough. They're in LV6.1, but I tried this in LV7.0 as well.
Rob