Performance does drive recruitment and retention. If somebody logs into SL and it operates as smoothly as the disk-cached virtual worlds/MMOs that they're used to, they're more likely to stick around than if they land in the world of gray blobs where it takes 60 seconds or so for the scene to resolve (even if they're stuck viewing a loading screen for that time... that's a metaphor they are used to).
Is it more important than cracking down hard on griefing or helping new users connect? Hell no. But there's a word for virtual worlds that focus on a single priority to the exclusion of all else: defunct.
Reticulating splines....