I was "into" arcade emulation for at least fifteen years before I finally built a cab for myself. Among my top 10 favorites of all time are Tempest, Missile Command, and Centipede. So it was a no brainer to make sure I included a trackball and spinner. I actually ended up with two spinners since I also figured that a universal cab that couldn't even play Pong properly would be a shame.
Part of the joy in having a cab is having arcade controls. When someone plays Pac Man on my cab it's certainly fun (and also in my top 10), but they know its fun on their PC too--or even their phone. But get them into a serious trackball frenzy with Centipede or Marble Madness, or a great spinner game like Tempest or Arkanoid, and they know this is a treat they're not going to be able to effectively duplicate at home.
Since building the cab, I've "discovered" many other games that use these controls that have made them well worth the investment. Millipede, Tac/Scan, Omega Race, Blasteroids, Cameltry, Wacko, Mad Planets, Tron, Off The Wall, Slither, Reactor, Quantum, Crystal Castle, Snake Pit, Rampart, Golden Tee, Shuuz, and Major Havoc among others. And of course, if you don't have a steering wheel, a spinner can work quite well as a substitute for certain racing games such as Pole Position, Night Driver, etc.
Naturally, if these games are a yawn for you, it would be silly to include these controls; but if even a few of them are in your top 20 list I'd strongly consider giving them proper support.