Go for the pro look with no spacers and a tiller length stem.
Agree that from an aesthetic point of view should be no more than 20mm, preferably less.
There was a long and very funny thread about Thorn's and stem spacers that ran to 30+ pages on the now defunct Cycling Plus - guy posted his Thorns and then took supreme offence and flounced around like a cycling Elton John when someone said that for them so many spacers was not a good look. At least twice, possibly three times he declared he was off and then just could not let it lie.
If I remember rightly Thorn deliberately design their bikes with short headtubes so you have to use a casino stack of spacers although I can't remember why. Regardless of any benefit it is really not a good look for me.
Ah yes. Can't have too short a stem either. Most of the mechanics where I used to work were of the opinion anything less than a 13 was 'unprofessional'. (If anyone wants a 13cm cinelli still have a couple floating about
) A road stem with rise is also not agreeable.
Can imagine a shorter headtube might somehow make the frame stiffer, and certainly lighter. However the big old stack would soon put pay to any stiffness benefits and as you say it looks a bit cack. Here's one fresh from thorn