I really don't see what the big deal is about the W204 interior. It's not cheap by any means. The visual build quality appears to be extremely high (small panels gaps) and the materials are more than appropriate. So the cabin looks a bit boring and bland - so what? That doesn't mean the interior is cheap. There is a big difference between cheap and bland/boring.
In fact, I think people should stop smashing and whining about the C-Class interior and examine the
overrated interiors of the competition. All interiors in this class are good - but some are over- and some are underrated. I think the C-Class interior is often underrated because people give it a quick glance without examining the detail - and the W204 interior has some amazing attention to detail. Hell, I've heard people make idiotic comments like
"My grandfathers Lexus LS460 is so much more comfortable than an S-Class! When we like drove from New York to Los Angeles we never like got out once because the seats were so comfy! But when I sat in an S-Class in a dealership for 20 seconds I already knew this was such an uncomfortable car. Even my IS250 is more comfortable!" <-- This comment actually exists on Youtube, except I exaggerated with NY to LA.
Anyway, the number one spot for overrated interiors goes to Lexus, in this case the IS. The IS interior has never impressed me. I mean it's a good cabin but in no way is it as good as people make it out to be. Here's why. It's a plastic fest inside - just like the C-Class, A4, 3er, G etc. Lexus uses shiny silver plastic and immediately everyone orgasms by going "Oooooh, ahhhh!" Is silver plastic more HQ than matte black plastic? It's still plastic, just differently colored. Second, the attention to detail in the IS interior is lacking. You have an extremely busy center dashboard with good attention to detail but the inside of the doors are virtually naked: they seem to have been taken from a different car. It doesn't match with the center console. Thus, the design harmony, IMO, is ruined. Third, the IS interior is not clean - it doesn't flow harmoniously like other interiors in this class. I personally hate this interior from a design point of view and I find the materials to be nothing special that warrant it being labeled as "superior or better" than its rivals.
In second place we have the Audi A4. For the most part I have nothing against the A4 interior. My only complaint is that this interior is also overrated. I find the A4 and W204 C-Class interiors to be almost like twins. Both seem well-made with extremely small panel gaps and both are often seen with the same dark gray, almost uninspired plastic dashboard color. The A4 only has an extra chrome strip here and there and a slab of wood here or there. Are you telling me that those little strips of chrome and wood make the A4 "expensive" while the W204 is "cheap" because it lacks this? Huh?

The A4 interior is a bit more flashy than the W204, that's all.
The addition of wood to the C-Class interior might actually be a bad move. After viewing Klier's chop, it just doesn't look right. I think the interior is currently fine as it is. What needs to be done is to add little chrome strips here and there, just like in the A4, because those little additions will really bring out the flashy side of the W204 cabin - without making it too flashy IMO.