Comes to show he's not "stupid" or "slow" like some think he is .
LBT 4 really showed this: Petrie and Ducky weren't sure whether to go with Ali or not after Cera said she might be lying, and had to ask Spike whether or not they should go. It makes you wonder whether if Spike jumped off a cliff they would too.
But anyways, Spike does have a song that predates this ("You're one of us now") but there it worked ok cause they didn't make his singing so...so
obvious, to the point where you couldn't really focus on the rest of the song