For Lucid Dreaming, the DP cost of Instill Doubt needs a minimum (unless you want to start instilling doubt in the Wis 1 buddies you brought along).
It's meant to only work on the guy whose dream you're inside (and only if it's not your
dream). I'll clarify that.
The idea is based on how suggestible your mind can be, even to the point of altering your perceptions. Even when awake, people can be led to believe (and even hallucinate) all kinds of untrue things, given the right conditions. In dreams, this is certainly amplified. Ever had the experience of thinking "well at least it's not X" in a dream, which then of course immediately causes
it to be "X"? That's what I'm shooting for. Basically, if you invade someone else's dream, you can then cause the dream to morph in all kinds of crazy ways just by suggesting those things to the dreamer.