"given that the next and previous links go nowhere" - do you mean you click them and it takes you somewhere silly? (like the same page, or something wrong). Or that they are there and unclickable, but you don't want them there at all?

They are there and unclickable so serve no real purpose with a singular item in a gallery.

I have no objection, but for some sites this would be perceived to break 'symmetry' across pages.
You can edit GALLERY_NAV.tpl with something like {+START,IF,{$NEQ,{N},1}}...{+END} around everything

Thanks for the example, I'll make the edit.