Ability to tell glissandos to have no text via style

That I'd either add them all as default, and in the end right-click one of them to select all similar elements. Then turn of the text in the inspector with a single command, which will affect them all.

Alternatively, I'd add one to a score, style it as I want and then add it to a custom palette so it can be reused whenever required.

I think you have a good point. People usually want *all possible gliss. shown or none.

*Some glissandos are too short and the text will never show. The user either has to live with it or make the measure wider so the gliss. is visible.

+1.

If there were textless lines built into the palette that behave as these lines already do, this would also solve the problem. I'm presently seeking and not finding this. The various "slide" lines don't maintain their position well when I change the stretch. Are the two "gliss." options in the Arpeggios and Glissandos palette the only lines which do this?

For single instances it's easy enough to edit the text in the Inspector, but even so, a built-in "port." (portamento) line might get some mileage too. IMHO the only good reason to include the gliss./port./etc. text at all is to differentiate effects from each other. It's true that there often is no room for the text anyway, which can railroad the composer into notating inconsistently or unclearly. e.g. Good luck with "fingered gliss.", "harmonic gliss.", etc., hopefully they are only attached to whole notes.

The more different textless lines are available (thickness, straight/wavy, etc.) and the easier they are to differentiate visually the better, as it is easier to present an index at the beginning of the score assigning each of these effects their own type of line than to cram in all that text.