I have a 2015 Boxster S. That was the last year the 6 cylinder was standard. The 4 cylinder turbo was instituted after that. I believe you could/can custom order a 6 cylinder, but it was very expensive.
I wound up with the car because my parents did not want a 4 cylinder turbo. They said it didn't sound right. So they got a 911 Targa, and now I have the Boxster. The 4 cyl turbos really do sound different.
I think my generation is the most aesthetically pleasing. I kinda feel more recent versions are too flashy (at least for my taste) and look more like race cars. Maybe that's just how people customized them. But I prefer the more classic look.
A trade off is my generation is really lacking in tech. I see this as a feature, not a bug, but if you like tech in your car, you'll want a newer model.
Some things to look for depending on how old you are looking:
1) Separation of the interior door panels from the frame - this is an issue in multiple year models that is easy (but not cheap) to fix.
2) A/C compressor - mine just went out. $3700 repair.
3) Leaks - engine and coolant. I've had both in the last few months. Not catastrophic or even bad, but again, expensive to fix. They are the result of plugs and gaskets degrading over time.
4) Engine fan malfunction (this would be the fans that cool the engine after you've turned it off). There will be a fault code if it happens.
5) If you decide on a Boxster, the dreaded convertible top fault error and corresponding malfunction (top gets stuck and the switch has to be toggled to go back into position). Also a corresponding fault code on this one.
I have a coworker with a CPO Cayman. I think it's a few years newer than mine. The last day of the warranty, the entire headliner fell. Deadlier replaced it, but had it been out of warranty, it would have been. $3-$4k repair. It's kind of a relief to know that's one problem mine won't have.
I know all this sounds terrible, but I love mine, and I think anyone you ask who has one will tell you the same. I plan to drive it forever.
Mine has had a thorough physical exam the last few months, and everyone who's looked at it has said it's in really good shape. The things I've mentioned above are par for the course when buying one of these cars. As long as you are prepared for a higher cost of ownership, it shouldn't take away from your enjoyment of the car.