I try to avoid watching speedruns before watching letsplays or playing the game, they sometimes skip 70% of what makes the game good. You lose the wow factor as well, it's less impressive and surprising when somebody makes a shortcut through 30 minutes of playtime. But depends on a speedrun.

I don't know what kind of streams you watched, but letsplays are less of a waste of time compared to that. Good letsplayers edit out the boring parts, streamers never do.