Ben,
Regarding your observation of your oil pressure, for sure, if you're seeing a drop, I too in your position would be thinking similar to how you do.
I don't see any change in pressure on the Nissan, other than for instance if I accidentally get the clutch out a bit too quickly from start, and the revs drop below what a normal idle would be. If I do that, yes the gauge drops momentarily.
But under normal use, even when the engine is fully up to temp, even at normal idle ( 750 rpm ), the oil pressure is always at the same place on the dial, no matter how many miles on the oil, etc.
As to "oil consumption", I've had engines over the years that used some oil ( two different big block GM engines, a 455 Buick and a 396 Chev )....and a few motorcycle engines that also used some. Other engines I've had used zero oil from new to when I sold them on. Go figure. In my case, all I can say was I broke them all in the same way, so I don't know why they were different. Back in the day, it was pretty common for big block GM's too use some oil. I never worried about it....just topped them up when they were a pint low, and drove them. Hard ( I was young and stupid. Now I'm old and stupid.... ).