The songs in New Vegas are mostly not as good but it's probably because the best songs for the 50's had already been picked for Fallout 3 so the choice for another game was limited. Hearing Fallout 3 songs in New Vegas would not have been good in my opinion.
3dawg was annoying but he had character, personaly I think 3dawg just had better lines to read from a script because while I don't have a problem with Mr New Vegas I find what he is saying not all that interesting so thats not his fault it's the dialogue he has been given to read out.
I agree all 3 stations having the same songs is a bit lame, I can sort of get that they might have the same songs for new vegas and wasteland radio because then if you don't like Mr New Vegas talking you can just swap to the other station and listen to the music. Maybe because you can stop the Rhonda & Tabitha station altogether they didn't feel it was worth featuring a completely new set of music.
The music and radio in new vegas is much better as ambient noise in the locations you visit so you only hear an occasional song or news update rather then permanently on your pip boy as you travel around in my opinion. This is how I prefer to play anyway.