Is there any major difference between the two?
Is it worth getting the Rooth?
I wouldn't worry; they should be quite different. The LS4 is thicker in the bass, and slightly relaxed in the treble, while being more prominent and upfront in the midrange. I'd say the midrange is more accurate than the Mage's..
You should have the Mage FR, right? This is an example of the LS4:
I actually quite enjoy the LS4 for its type of signature.
The Mage is, well, let's just say I think the Miracle sounds nicer.
Sorry, can't help you here; I haven't heard the DN-2000. I do like the DN-1000, though.
I also haven't heard the 5.0, so it's difficult for me to make any recommendation one way or another.
Average_Joe also has impressions of the LS4, so you can consult that to help you make a decision as well.