Very informative stuff in here - thanks everyone! Yes - I think there are some mitigating factors at play here. Typically my drive roundtrip is ~ 6km, so there's hardly much time to warm up the motor at all. Not to mention it's getting cold outside -- only about 4 or 5 degrees C out. I think those two things alone might account for my slightly lower than expected fuel economy. Probably the most important thing I can do is check my tire pressures, in this situation.

On a different note - I have lately heard some "new" noises under the hood. It sounds almost like increased valvetrain / exhaust noise, and it only manifests itself in a small range of rpm's - only between about 900 - 1000 rpm. I am not sure at all how best to describe it... almost like a resonating exhaust noise that I can her over the usual (totally normal) engine noise. Upon investigation, I noticed that the fitting and hose leading from my valve cover to the air intake / cyclonic oil separator was totally loose and disconnected. Putting it back together (to the best of my ability) seems to have greatly diminished the noise. I presume this is probably the logical source of what I'm hearing - and I presume the parts are equally trivial to replace, since the flexible rubber hose on the air cleaner itself seems good, but the hose from that to the valve cover fitting seems shot (no matter how much I fiddle, it just doesn't make a good positive connection anymore).

Believe it or not I was actually scouring my factory engine manual to try and find a part number for that, but came up empty