The whole idea of B4 was done very stupidly. Hamhandedly written in, and it reduces the uniqueness of the achievement of Data and Lore.The only problem is that Data isn't really dead. His identical brother, B-4, has all of his memories. I bet if Nemesis was a hit, 'Data' would have been back for another movie.
TATV doesn't really count since he wasn't on screen, and he probably spent all of about 20 seconds recording his lines.
Triplets? Groan
I think part of the problem with the B4 concept was simply because the main story was already about a double of one of our heroes. Sure, I've heard the reasoning that it was to set up parallel struggles between Picard and Data, but it would've been good -- and cleaner -- if plot A and plot B weren't so similar (it works in novels and comics b/c of room, but it's difficult with the time constraints of a movie). With that said, get rid of either the Shinzon or B4 storyline and the other would have perhaps benefited from more time for development.