You asked a number of questions; only one is answerable by completely
uninformed opinion, so that's the only one I'm qualified to respond to.

>  Would it be absolute heresy for me to have a white top on a late model
>  Westfalia?
>
>  Dan

If that's what you want, I think you should do it, because:
(1) It's your van, and that's what you want.
(2) It's more practical than the body-colored top.
(3) It's un-doable.  That is, if you or some future owner
    of the van got hit by a sudden attack of "everything must
    be factory original" obsession, the solution is simply to
    repaint the top.  It's not like you're cutting into body panels
    or something.
(4) VW vans have a long tradition of custom paint jobs.  Just
    imagine the conversation you can have with bus owners at
    your next Grateful Dead concert:
    "Hey, man, I just put new custom paint on my VW van."
    "Cool, dude"
    "But it's pretty radical.  I'm kinda worried about it.  It may
        just be too wild."
    "Really? What did you do?  Peace signs covering the
        windshield?  Too many marching rainbow bears?"
    "No, I painted the pop-top white."
    "Uhhhh.... aren't they all white?"
    "Not that year.  Factory spec was body colored."
    "Woah, dude!   You ARE a wildman!  Will you show
        me the van?"

                             -Steven Sittser
                              Dark gray '88 Westfalia
                              with matching roof - impractical,
                              but I think it looks spiffy.