Among the other suggestions listed here...
I recently wound up inheriting an old iMac that came To me with El Cap installed. Ran like a dog. An old dog. With three legs. But it had snow leopard discs in the box. Out of curiosity, I blew the machine away, installed a fresh image of snow leopard. Amazing. The machine is fast, stable, beautiful, and all the graphics are colorful, deep, gleaming, and rich. You've gotta try it and see how nice OS X can be. It's fantastic.
iTunes fires right up in under a second, doesn't beachball, is organized in an immediately comprehendable intuitive design laid out sensibly in a straightforward and consistent design language. It plays instantly, plays several kinds of videos just fine, and it hasn't crashed once. The miniplayer works and isn't broken three different ways. There aren't four kinds of UI controls operating in tandem like an MC Escher puzzle. And it has Front Row and a remote that can be operated in the dark by feel and never needs connecting or syncing or special network access bs.
I wouldn't have bought one of these before today, but I am definitely keeping this, if for nothing else than a better Apple TV. This machine has been running nonstop for over a month and hasn't slowed down or skipped a beat. Everything on it indeed just works. It's shocking how nice this old system is. And sad at how far OS X's UI has been allowed to slide.
Rebuild iTunes so it does what you want it to, and the Ui resembles iTunes a decade ago.
Add a Front Row widget because it's great.
But mostly bring the quality up to where it was a decade ago.
And quit trying to tur it into an iPhone accessory.
Also, try using your OS without an internet connection before publishing it, to see what hell your rural customers are going to be stuck in when whole parts of the system don't function and crash.