interestingly I was planning to build my arcade machine with either an NUC or a Thin-ITX case.
the main advantage of NUC is weight, its only 1KG, whereas the thin ITX cases are 2KG, this is assuming you are going down the fanless route, which I am.
main disadvantage is that its not very upgradable, and it's not quite as powerful as desktop CPUs, the thin ITX cases can still take descktop CPUs at 45w.
also there are only 4 usb ports in the NUC, whereas the thin-ITX has 6, so in the case of 2 light guns + sensor thats 3 usb ports already! don't forget your USB speakers so yeah.
weight is quite important if you are planning to mount it to the back of your monitor, which is what I'm planning on doing with a 19" 5:4 as I will just letter-box to 4:3.
also when you buy a monitor it has to not have a height adjustable stand, they are the only ones that have the screws available for an NUC mount, when I say weight is important I meant for your ability to lift it easily, the monitor should easily hold a 2.5KG PC on it.
I'm still undecided between the two, do you think I could run Pcsx2 and dolphin games on an NUC CPU?