Serblinfan
Some great comments already, and I'll only add my experience. Better cables can absolutely improve SQ, but only if the component is capable of taking advantage of the better cable.
Better cables can also make a system's SQ worse, if they are very revealing and the components are below the quality level of the cable. Better cables color the sound less, and usually are more transparent and more revealing....they will not hide any warts so to speak.
However if you are on the "never ending" upgrade path (as I am), my system tends to "grow into" the better cables as I upgrade components. I however do not own extremely high end cables, those costing thousands of dollars.
In hind sight, I would have upgraded my digital cables first; they gave the largest upgrades in SQ. From there interconnects and speaker cables were about equal, and lastly power cables......however they all made noticeable improvements.
Also pay attention to what type of cable you are using for a specific application, and use that type of topology. For digital components, is your equipment optimized for USB? AES/EBU? I2S? For XLR/RCA are your components fully balanced, or am I using a longer cable run that XLR would better suit.
Some companies optimize for a specific connection, and that is usually the preferred type to use. Pay attention to the limitations of a certain topology. Most DACS/DDCs/streamers will publish their specs on a specific connection.