Has to be joke? It's an open air enclosure. There are tens of thousands of arcade pcb's that were encased in plastic with little to no ventilation that still function 100% today. Point of fact - the most reliable pcb's are the ones that are in cartridge enclosures.
But yeah a lot of those case based pcbs from my experience generally have fewer ic's than boards without cases (unless we are talking about games that came in big ass computer cases). That alone probably contributes to why more are working vs boards with a shit ton of ic chips. When I think of games that came in cases I usually think of MVS,CPS2,PGM,some JP CPS1 games, F3 and then you got the computer based case hardware. There is a lot more of course. At least it isn't nowhere near as bad as what fuck tard Luke morse did where he made enclosures for all his games that he calls "PCB sandwiches" or people running their games in bubble wrap baggies like the ones you see from Japan shops.
the point I was making is if you keep that horizontal and play for extended periods of time the ambient temperature is going to be much higher than say, having it caseless. Whether that affects the lifespan of a game that has been on for years on end in any meaningful way is really unknown. Thermal cycles are really what kills games imo. A lot of these boards really should've been fit with heatsinks and had fans as its really thermal cycles that destroy these games
I think the acrylic case idea is good overall, it removes mechanical stress from the equation and makes swapping boards ez. I just hope you used anti-static acrylic as it can build up a big ass charge over time and POTENTIALLY kill your boards. Does anyone remember when Chempop pointed this out at the collectard cave acrylic case thread over here?