I do really notice it with our Mini Cooper. Just the weight and feel of the doors when you close them, you wouldn’t think it would be so for such a small car. But it feels solid. And the feel of the materials are a much better quality when I compare them to my parents’ Altima or a G35 I looked (for a friend).
If you think the Mini has solid-feeling doors and a vault-like interior, you need to spend more time in...well, anything German besides the Smart Car

Because the aspects you describe are generally not regarded as the Mini's strongest points. To the contrary, I've often heard them criticized in the Mini. Now it's handling and adrenaline factor, on the other hand...hard to beat.
The 2008 C-Classes I drove weren't the fastest or the most exciting, but they were rolling bank-vaults. Incredible feel if that's what you're looking for. And the 2006 325i I test-drove just felt...special. I had some mind meld thing with it, and it telepathically knew what I wanted and did it, keeping me constantly updated with clear feedback that was never harsh.