30 fps is the standard "Optimal" level, below which the eye percieves imperfections.
It makes sense to adjust the X-Plane settings (without any addons installed), to achieve the best performance from both graphics card and cpu to the 30fps benchmark.
It is then a decision, or tradeoff as to whether you use an addon (particularly weather) and suffer lower settings within X-Plane to achieve this.
Every simmer would love to run at 60fps with all sliders at Max, but this will be a long time coming, perticularly with Moore's Law no longer true. With such a vast area to draw, sims demand unique levels of performance.