I think that too. Although other activities can learn how to work more effieciently or quickly, etc...Disclaimer: I haven't read the thread.
A psych major I know told me that "brain training" like cubing will help you get better at cubing, but not other brain activities. My personal experience seems to confirm this.
As instance, music taught me to work slowly and precisely before working faster, programing made me way more organized and clear.
All these little things result in me working with more efficient manner and also faster, the organization has been a great improvement.
For cubing I don't really find any help I had with it.