50+ is a lot more difficult than going through it with a new character on a different alliance. A lot of can be bring-a-friend necessary in order to progress. It's like playing the other alliances through on a higher difficulty setting that encourages grouping.
When you are in the other zones, the dialogue is the same, as if you were playing through it for the first time.
No, I believe the words when you go to take the quest to travel to the other alliance is something like "It will be as if you are a soulless person traveling through the realm.... no word of your deeds will have reached them.... etc."
So, basically back to the beginning, only a lot more tough.