Essentially, the payoff for doing all those things wouldn't exceed the consequence. Many people make use of Dashboard, Spotlight, and the others (myself included). If the script disabled them, the usual reaction would just be to undo the changes, in the process bypassing everything else being offered.
And Dashboard isn't even using any resources at all if you simply do not open it. If you do, the widget DashQuit is very useful for actually quitting back out of it.
Believe me, I've already pondered this road during development...
Yes, the things I mentioned shouldn’t be enabled for everyone by default. I use spotlight a lot too by the way.
Thanks