3x Ferraris and still DIY'ing your E53.
Awesome.
I'll just throw in my data point from my 2001 3.0i - ~194k miles. Original oil pan gasket and engine mounts. I had the head off a couple of years ago and did a ton of other work "while I was in there", kind of looked at the engine mounts, would have been easy to replace, but no problems so I just left them in there. Still no problems. Smooth.
I can't say the bottom of my engine is dry (at all), but that's what the stiffening plate is really for, right?
The rate of oil loss is not significant, and I park on the street.
But it has lived a pretty easy life here in CA. Roads are pretty good, climate is great. So YMMV.
On your specific vibration, I'd look at the things you know trigger the problem = AC, fan. Also vary RPM to see how it changes. Sounds and vibrations can be amplified by resonances to make them seem worse than they really are. And yes, better engine mounts will help all of that, but may not be absolutely necessary.