A very usefull option could be an option that permit to automatically minify js and css script using :
Because I notice the more you add plugin the more css and js scripts inclusion you have in it.
Dealing also with the css and js coming from other installed plugins.
Which leads to slow down you wordpress site.
Moreover a gzip compression of css and js would be also great!
With that 2 options we should finally get some good score in Yslow! ;-)
I know this stuff should be done by tweaking:
and associated function files
or may be with some action and filter in a plugin.
But not experienced enough to make a great plugin and not enough time...
So Could you dig that way?