The thing that drives me nuts about both the transporter accident and the engine imbalance/wormhole thing is that they're both setups with no payoff. Neither one ever comes back into play or plays any sort of role in the plot. It's just "Aw geez, those two crewmen are dead, oh well, we've replaced them now! Cool!" and "The Enterprise isn't working right, oh wait, we've got it fixed now! Cool!" and then neither one is ever even mentioned again. So why waste all that time in the first hour of the movie establishing either issue, then?
Neither one of the transporter casualties is anyone that we particularly know or care about. There's never even a shot of Commander Sonak getting into the transporter on his end to remind us that he's the same guy we saw in the tram station scene that introduced Kirk. I doubt that a lot of people even remembered Commander Sonak's name on their first viewing, and the female navigator who dies never even gets a name in the finished movie. And less than ten minutes later, the deaths are all forgotten about so we can the flat joke of "Oh look, McCoy still hates the transporter, isn't that cute? He's so irrational and eccentric!"
And then engine imbalance thing, same deal. It never comes back into play later, like when V'Ger is transforming and the Enterprise has to get out quickly. If the engines failed again at a critical moment during the mission, that could've added some more much-needed suspense and jeopardy to the film. Not of the vague "That thing is 20 hours away from Earth" variety, but of the "Scotty! I need warp speed in three minutes or we're all dead!" variety. TMP needed a lot more of that.