Yes, great suggestion it would certainly need few settings so admins can configure everything.  

I'm not sure what do you mean by "skins could then hide ones they don't want (btw seems controls need a ThemeId to be able to do it?)" ?

Regards

I meant that web.config setting is best, but if one wants to show both only at some pages, they'd set the both option at web.config and hide the pager at some pages using a custom theme for that page

however I think at theme you can't set an ASP.net control property like visibility for some control using its id, but the control needs to have a ThemeId (was called something like that) attribute set to be able to refer to it from a theme. Probably MS did that for security reasons. Of course could also specify CSS classes like pager-top and pager-bottom and hide from CSS with a custom theme for specific pages where you don't want both pagers if in web.config you opted to show both

For "per page" settings we use the WebPart personalizable properties that can be set pet WebPart (dynamically if it is in a zone, or manually if not).