Well, no. Being psychic is not like having a radio signal that a nonbeliever can block with a screen. I mean, I also make soap, and I would not hesitate to make soap in a room where someone said they did not believe in soapmaking. I would cheerfully sing in the room with someone who did not believe anyone sang soprano anymore.
The presence of a skeptic would mean that I would choose not to read for that person, because they obviously don't feel invested in the process. The skeptic would not be a reason that I would avoid offering any reading at all.
By the same token, I would not immediately choose to include the skeptic, if I were given a chance to select the audience. The skeptic can make sort of a blank space in a room that is filling up with high-frequency vibrations. Visualize that as a single stone standing up from the bed of a river. It doesn't block the flow of the river, but it creates an obstacle that diverts the river's path.
That said, I don't think there is anything wrong with being a skeptic. I firmly believe that there is a place for skepticism within our panoply. And of course, you may be aware that I am both a psychic and a skeptic; passionately devoted to continuing to ask which parts of this are real.
I simply note here that skeptics can create other challenges if they refuse to consider the possibility that something could be real. Whether or not you commute the disbelief to something else, refusing to hold space for the possibilities is a heavy burden to bear, it seems. Too heavy for me, by a long shot.
If the question is, "Does it matter?" I would answer that yes, intention always matters. Intent is the lightning rod that attracts experience.
But if the underlying question is, "Does a lack of belief change the baseline ability to ____________?", then I am bound to answer no. Believing does not change what a thing is, and it cannot change the parameters of--well, anything.
Ability carries its own energy. Believing is separate.