There's no consistent parameter handling for most includable special pages. In the case of Special:Newpages, the following should work:
{{Special:Newpages/namespace=XXX/limit=XXX}}
I'm afraid that doesn't work; adding the namespace parameter returns the same items as when using no parameter at all.
It seems there's only one parameter: If I use {{Special:Newpages/#}} then # items will be returned. Unfortunately, that doesn't help me here...
-- F.