"but even i'll admit that AmigaOS 1.0 to 3.9's default look is shockingly bad."
I'm one of those guys that think every AmigaOS up to 3.9 looks great.
AmigaOS 1: wow, blue colors, quite nice and big icons. I like it. Easy to see what I'm doing.
AmigaOS 2: Ok, now we're running the grey power here. Still nice and intuitive icons.
AmigaOS 3: Hm, still grey? Allright! I'll just smack this image to the background... aaah, nice and pretty.

AmigaOS 3.9: Oooh! Now we're talking! This is looking GRRRReat! (I have themed this look to my win2K computer so every computer I use look Amiga'ish)
But that's just me...

and adding:
AmigaOS 4: Yes! They haven't changed the appearance that much! This is great, this looks good and I can change the appearance if I want to, like um.. you know, into OS3.9 colours. ;p