I have followed some reference designs that uses crystals like 40 MHz for the MCU, and I have not considered the trace width to do impedance matching. The result is that the boards works fine (I kept the track as short as possible). I have not seen any note anywhere that one should consider trace width to have an impedance matching (or at least get closer to it) as above 3 MHz is considered high speed signal. I wonder why one does not consider the wave reflections on the crystal's traces? I don't see any note about it on crystals' datasheet neither.
Even if the reflected waves does not change the frequency of the oscillation, it should cause more noise in the board am I wrong? Even if one would not need to use extra L-C matching circuit for it, but at least wouldn't it be better to use a little bit thicker or thinner line width to improve the reflection depending on the crystal and MCU?