Well, with my first build I was super anxious to get as much as possible in, just "because I can" - and that included the artwork as well.
So it was Final phantasy sideart (?!, yes, I love Yuna, but have never played the game

), Bubble bobble CPO, some Donkey Kong, Space invaders and Pacman characters at the bezel and as the icing on the cake there was Mario Bros in the marquee. At least I had the sense of doing everything in the same blue shade

Later on I did a restoration, and without any shame I totally ripped off the design from Koenigs Wee Cade. A clean design indeed.
For my Minicade I was even more simplistic, doing no CPO at all

So what is my point? Less is more

And the genuine artwork in the 70's and 80's was often pretty simplistic. Maybe not that much by design, but the consequence of primitive technology and cost savings. Usually it was made of stencils and screen printing, and that only allowed simple graphics with few colors. So when you mimic that style it feels more authentic to me.
I second what others has said already - stick with a theme. And keep it simple. If you need to show off all the games, do that on the monitor with a fancy frontend and attract screens
