Well, B-4 was unnecessary to begin with. Data's death was unnecessary also. Wouldn't a well placed overloading phaser also destroy the weapon? Data could have slapped that stupid little transporter thing on Picard and then hugged him, beaming both of them out. I didn't find Data's death sad because it a) had an obvious out and 2) it clear this was just following the Khan template. Paint by Numbers Trek.
Spock's death actually worked for a number of reasons; he had his goodbye with Kirk; Kirk was shattered; Spock's death was part of his character growth. In fact, it was part of Kirk's as well. There was some very rich character development there, something Nemesis didn't grasp.
Was it sad? Nah, not for me. I had no doubt there would be another Star Trek movie and Spock would be brought back. There wasn't anything official to justify that, just a bunch of TV death cheats I sat through all my life. That's back when I was too young to be in the loop with the makings of Trek II and had no idea they never intended to do a third film, let alone a whole series. The cluelessness of youth made movies a lot more fun.