Just to add my 0.02USD:

I think my preferred course of action would be to enable '-n' by default and deprecate/ignore the option.  For the assert output on stderr, I think it would be fine to hide it by default, but show it if verbose > i for some value of i (0 or 1, probably).  They really don't add much except spam in the buildbot logs.

Also, for the record, changes to how the buildbots are called isn't very hard; let me know if any are needed.  I'd like to eventually get rid of Tools/buildbot and just let the buildbots call the same things the same way users do.