I recently read an article on World-science.net that, as a psychologist and as a practitioner of "alternative spiritual practices" that interested me. It basically proves that superstitions, such as lucky charms, really do work on a psychological level to improve performance. The owner believes that it helps, so it does.
Even though I am both a theist and a Druid, this is similar to how I view prayer and spellwork. It helps us because we believe it does. I do believe Pleroma(and any other entity someone may pray to) hears our prayers, but it is our belief in such systems that do the most help - after all, if you don't believe in God, you wouldn't bother praying to Him.
Likewise, the bulk of a spell is the Witch's or Druid's belief that it will work. If one book/website says to use one ingredient for the spell, but another one feels more right to me, as the one performing it, I will use what I feel more comfortable using, otherwise I would be distracted by using something that didn't make sense to me. I limit most of my spells to things that involve drawing something to me(like drawing good luck), driving away something(like obstacles or bad luck), or geared towards changing my mindset, because those are what I believe work most, as they are meant to change my viewpoint or perspective. While I may pray for rain, I don't do a spell to make it rain, because I don't believe that works. If it's meant to rain, it'll rain.
In all, some superstitions or 'magical thinking' isn't bad. How dull would life be if everything could be explained?