I'm surprised that no one has made this clear to the OP. Generic inner cables are of lower quality manufacture. The metal alloy (galvanized steel? Not sure) will most certainly corrode after a season or two. Also, the cables are not die drawn to create a smooth outer surface. The result is a cable that darkens and has friction. The best inner cables are at a minimum stainless and die drawn. Other very good cables have various coatings (like Teflon) to minimize friction. I've used these, and they can be quite good. They tend to be stiffer, which may be a problem depending on the bends that your cable must take.

Outer brake housings from generic (think Bell) cable kits have are simply wound steel covered by a colored rubber layer. These are not lined. Nor are they rigid enough. There is a big difference between good quality lined housing and generic dime-store housing. For indexed shifting greater than 8-speed, you need rigid compressionless housing that's made with longitudinal strands, lined, and with good quality ferrules at the ends. A good kit will contain the proper ferrule tips to mate to STI shifters and to various kinds of stepped-down cable stops (for internally guided cables, for example).

Don't go cheap if you plan to keep and ride the bike. If you plan to flip the bike, then let the dictates of your character determine what cabling you'll choose.