Instead of setting a page to 'not show in menu' you can untick this box so that it shows in the menu and then exclude it in your menu manager call using excludeprefix in your page template (or wherever else you are calling it) i.e:
I believe (not 100% sure) that pages that are excluded in menu manager like this (but still set to show in menu) should then show up in the next/prev links. More info on Menu Manager can be found by going to Layout > Menu Manger > Help (top of the content area in admin)
I tried the solution you mentioned in another thread with limiting the number of menu levels, worked a charm!
Code used for a 4 level menu to limit the products from displaying in the menu but keeping the relational links working between the level 4 products: {menu number_of_levels='3'}