I like mirc's simple interface. I'd rather keep mirc useful, small download and small footprint than fill it full of 'bling', bogging it down and making it like windows xp (teh pretty making the whole thing so much slower).
There are enough scripts, dlls and etc around to change mirc looks and abilities radically.
If you want your mirc running like its on a 486, be my guest, don't assume the rest of us do.
