When Lou realizes "Home Sweet Home" is playing as he is in the garage he really is getting down to it as if he's just happy the song is on... but later you realize he was planning on dying.
Nick, Adam, and to a lesser extent Jacob are all going to have no idea what they're lives have been like over the past twenty years. What if April mentions something about her and Nick's wedding? He's going to barely know her.
They could always ask Lou
Originally Lou has been erased from the timeline and replaced by time travel Lou. The other three might have had full lives and still have memories of both timelines that get meshed when they returned to the present, but original Lou is gone. Sure it sounded like his life was shit, but that's still pretty dark.
The squicky kind when you watch the almost-threesome scene knowing that Jacob is Lou's son.
In the sequel, the killer car received permission, possibly from a human being, to kill its target. It was implied this isn't the first time this has happened to someone in the future and that murder by sentient cars is a common danger.
Every time Lou is about to have sex with anyone other than Adam's sister, he is prevented in some way. First, Jacob refuses to do a Three-Way with him, the second time a squirrel runs onto the field of the NFL playoffs and changes the outcome of the game, thereby making Lou lose his bet (He would have received a "classy blowjob") All of this ensures that Jacob would have been born, since the semen that would have otherwise made Jacob would have been wasted. Basically time itself is making it so Jacob can be born to go into the past as a cyclical loop.
In the first movie, Lou mentions how if he wanted to kill himself he'd be amazing at it, saying he would shoot off his dick, and guess what happens to kick off the plot for the second movie...