omega,
in postlist.php, look for
if ( !$cs ) { $cs = 2 ; }
If you change that to
if ( !$cs ) { $cs = 2 ; }
The result will be that by default, you will see calendar boards in their "hide calendar" mode, and you would have to click on "show calendar" on top to see the calendar. So it wouldn't "stare you in the face".
As for blank fields for Bo_Calendar for non-calendar boards, yes, that's OK.
Regards,
Max