>ton of bugs
Not a "ton" but maybe a few pounds?
CS6 Bug Clip Name http://forums.adobe.com/message/4654667
As for OnLocation... if you don't un-install CS4, you will still have OnLocation
>take my laptop on location
Do you always have an Internet connection when you are on location?
how is that done if Creative Cloud replaces my existing CS4?
CS versions do not replace each other. They get installed along side each other so you can easily have multiple versions of the software on the same machine. Many people do this.
Compared to CS4, are the features worth it
Overall, YES! But there are some bugs and quirks in CS6 that didn't exist in previous versions. Your best bet is to install the trial and give it a go.