Right.
First of all, thanks for all suggestions, guys!
I visit this forum sporadically nowadays, maybe once a month at best. Great to see my post still active.
As for rattles, no solution found (though I will now follow up on all your latest suggestions). I have rattles from the front (less now when it is warm, the plastic has expanded, I guess), from passenger door, from driver's door (from time to time). TERRIBLE rattle from the back. During service at VW I asked them to handle this issue, they checked and said it was tailgate (or something back there, I don' remember) and they tried to fix it. It did not work.
I've been in a Skoda Octavia with 140000km on it and which is driven much more aggressively than my E30. I've been in a rental Polo. They were both dead silent inside.
I'm swamped with other things in my life, so I care much less about rattles now, and I listen to music in the car, so that kills the ugly sounds as well. But still, the feeling of badly screwed together interior is there...