I suggest to disable the [X refs, Y blocks] ouput in debug builds by default, and provide an option to enable it if/when necessary.
Most of the time these values are not necessary, and they end up getting in the way while copy/pasting code from the interpreter and/or running tests (we even have a function in test.support to get rid of them).
They are sometimes useful while investigating refleaks, so there should still be an option to enable it.  I'm not sure what would be the best way to do it (a new python flag?).