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I've also got the Espresso/Cognac interior, although my paint is Mahogany Brown Metallic. I think the interior would work very well with Night Blue. I had a Midnight Blue Metallic 996 with Natural Brown Leather interior, and it was awesome.
I had a midnight blue 997 C4 with cocoa interior. I loved it when I first got it, but got a little tired of it over time.
A friend has a 987.2 Spyder in Arctic over Silver, and I've never grown tired of it—but when I look at the photos above, I can see what you mean. My first impression is WOW, but maybe I would get tired of it too. Cocoa has a lot of red in it...it's quite strong. I see Espresso has having a lot of gray to it, and being so dark that, from outside the car, it often looks black in photos. It might therefore be less likely to get old with blue. But the point you raise may given an edge to Agate Gray Metallic on Espresso, as gray/brown gives you just one color instead of two.
Have you considered Chalk exterior to match the interior stitching? If you have a lot of dark black exterior bits (rims & headlines), I think chaulk would look good as well.