G'day Pär,
I must disagree with you on this one - one of the most useful aspects of headless notes is that you can supply your own heads as text.
As an example, Robert A. has created a set of scripts that allows placement of round noteheads (specific request) and for heads containing letters (note names - another special request).
If headless notes were treated as being non existent for note spacing for printing purposes then this functionality would break.
Incidently, I've just notated a transcription of the Overture to William Tell [here on the scripto] where I've used headless, invisible notes to position a slur, using extra note space, and it worked perfectly. If the extra note spacing had not worked, the slur would not have positioned correctly. The relevant bars are in the clips below.
Lawrie
Staff 1 (to be layered with staff 2):
!NoteWorthyComposerClip(2.0,Single)
|Clef|Type:Treble
|Key|Signature:F#
|Tempo|Base:Eighth|Tempo:60|Pos:16
|TimeSig|Signature:3/8
|Dynamic|Style:p|Pos:-12|Justify:Right
|Rest|Dur:32nd|Opts:Stem=Up,VertOffset=6
|Text|Text:"poco"|Font:StaffItalic|Pos:-15|Placement:AtNextNote
|Note|Dur:32nd,Staccato|Pos:-2|Opts:Stem=Up,Beam=First,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:-5|Opts:Stem=Up,Beam,ArticulationsOnStem
|TempoVariance|Style:Accelerando|Pos:-15
|Note|Dur:32nd,Staccato|Pos:-2|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:0|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:2|Opts:Stem=Up,Beam=End,ArticulationsOnStem
|Note|Dur:4th|Pos:5^|Opts:Stem=Up,Slur=Upward,ArticulationsOnStem,Tie=Upward
|Note|Dur:8th|Pos:-7|Opts:Muted
|Bar
|Note|Dur:32nd,Staccato|Pos:5|Opts:Stem=Up,Slur=Upward,Beam=First,ArticulationsOnStem,Tie=Upward
|Note|Dur:32nd,Staccato|Pos:-5|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:-2|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:0|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:2|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:5|Opts:Stem=Up,Beam=End,ArticulationsOnStem
|Note|Dur:4th|Pos:7^|Opts:Stem=Up,ArticulationsOnStem,Tie=Upward
|Note|Dur:8th|Pos:-7|Opts:Muted
|Bar
|Note|Dur:32nd,Staccato|Pos:7|Opts:Stem=Up,Beam=First,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:-2|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:0|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:2|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:5|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:7|Opts:Stem=Up,Beam=End,ArticulationsOnStem
|Note|Dur:4th|Pos:9^|Opts:Stem=Up,ArticulationsOnStem,Tie=Upward
|Note|Dur:8th|Pos:-7|Opts:Muted
|Bar
|Note|Dur:32nd,Staccato|Pos:9|Opts:Stem=Up,Beam=First,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:0|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:2|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:5|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:7|Opts:Stem=Up,Beam,ArticulationsOnStem
|Note|Dur:32nd,Staccato|Pos:9|Opts:Stem=Up,Beam=End,ArticulationsOnStem
|Note|Dur:4th|Pos:12|Opts:Stem=Up
|Rest|Dur:8th|Opts:VertOffset=-8|Visibility:Never
|Bar
|Dynamic|Style:p|Pos:-16|Justify:Right
|Note|Dur:16th,Slur|Pos:0|Opts:Stem=Up,Crescendo,Beam=First
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Up,Crescendo,Beam
|Note|Dur:16th|Pos:2|Opts:Stem=Up,Crescendo,Beam=End
|Note|Dur:16th,Slur|Pos:0|Opts:Stem=Up,Crescendo,Beam=First
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Up,Crescendo,Beam
|Note|Dur:16th|Pos:2|Opts:Stem=Up,Crescendo,Beam=End
|Note|Dur:16th,Slur|Pos:0|Opts:Stem=Up,Crescendo,Beam=First
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Up,Crescendo,Beam
|Note|Dur:16th|Pos:2|Opts:Stem=Up,Crescendo,Beam=End
|Bar|Style:Double
!NoteWorthyComposerClip-End
Staff 2:
!NoteWorthyComposerClip(2.0,Single)
|Clef|Type:Treble
|Key|Signature:F#
|TimeSig|Signature:3/8
|Note|Dur:8th,Slur|Pos:-2|Opts:Stem=Down,Slur=Downward,Tie=Downward
|Note|Dur:16th|Pos:2z|Opts:Stem=Down,StemLength=1,XAccSpace=1,XNoteSpace=3,Muted|Visibility:Never
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Down,StemLength=12,Beam=First
|Note|Dur:16th,Slur|Pos:-11z|Opts:Stem=Down,StemLength=1,Beam,XNoteSpace=1,NoLegerLines
|Note|Dur:16th,Slur|Pos:-11z|Opts:Stem=Down,StemLength=1,Beam,XNoteSpace=1,NoLegerLines
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Down,Beam
|Note|Dur:16th,Slur|Pos:-5|Opts:Stem=Down,Beam,XNoteSpace=2
|Note|Dur:16th|Pos:0|Opts:Stem=Down,StemLength=14,Beam=End
|Bar
|Chord|Dur:8th,Slur|Pos:-7,-2|Opts:Stem=Down,Slur=Downward,Tie=Downward
|Note|Dur:16th|Pos:2z|Opts:Stem=Down,StemLength=1,XAccSpace=1,XNoteSpace=3,Muted|Visibility:Never
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Down,StemLength=12,Beam=First
|Note|Dur:16th,Slur|Pos:-11z|Opts:Stem=Down,StemLength=1,Beam,XNoteSpace=1,NoLegerLines
|Note|Dur:16th,Slur|Pos:-11z|Opts:Stem=Down,StemLength=1,Beam,XNoteSpace=1,NoLegerLines
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Down,Beam
|Note|Dur:16th,Slur|Pos:-5|Opts:Stem=Down,Beam,XNoteSpace=2
|Note|Dur:16th|Pos:0|Opts:Stem=Down,StemLength=14,Beam=End
|Bar
|Chord|Dur:8th,Slur|Pos:-7,-2|Opts:Stem=Down,Slur=Downward,Tie=Downward
|Note|Dur:16th|Pos:2z|Opts:Stem=Down,StemLength=1,XAccSpace=1,XNoteSpace=3,Muted|Visibility:Never
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Down,StemLength=12,Beam=First
|Note|Dur:16th,Slur|Pos:-11z|Opts:Stem=Down,StemLength=1,Beam,XNoteSpace=1,NoLegerLines
|Note|Dur:16th,Slur|Pos:-11z|Opts:Stem=Down,StemLength=1,Beam,XNoteSpace=1,NoLegerLines
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Down,Beam
|Note|Dur:16th,Slur|Pos:-5|Opts:Stem=Down,Beam,XNoteSpace=2
|Note|Dur:16th|Pos:0|Opts:Stem=Down,StemLength=14,Beam=End
|Bar
|Chord|Dur:8th,Slur|Pos:-7,-2|Opts:Stem=Down,Slur=Downward,Tie=Downward
|Note|Dur:16th|Pos:2z|Opts:Stem=Down,StemLength=1,XAccSpace=1,XNoteSpace=3,Muted|Visibility:Never
|Note|Dur:16th,Slur|Pos:-2|Opts:Stem=Down,StemLength=8,Beam=First
|Note|Dur:16th,Slur|Pos:-12z|Opts:Stem=Down,StemLength=0,Beam,NoLegerLines
|Note|Dur:16th,Slur|Pos:-11z|Opts:Stem=Down,StemLength=0,Beam=End,NoLegerLines
|Note|Dur:8th,Slur|Pos:-7|Opts:Stem=Down,XNoteSpace=1
|Rest|Dur:16th|Opts:Stem=Down,VertOffset=6|Visibility:Never
|Bar
|Chord|Dur:8th|Pos:-7,-5|Opts:Stem=Down,Beam=First
|Rest|Dur:16th|Opts:Stem=Down,VertOffset=-8|Visibility:Never
|Chord|Dur:8th|Pos:-7,-5|Opts:Stem=Down,Beam
|Rest|Dur:16th|Opts:Stem=Down,VertOffset=-8|Visibility:Never
|Chord|Dur:8th|Pos:-7,-5|Opts:Stem=Down,Beam=End
|Rest|Dur:16th|Opts:Stem=Down,VertOffset=-8|Visibility:Never
!NoteWorthyComposerClip-End