Porsche's original intent with the Cayman was as an entry-level model to 1) lure people who want a new 911 but can't afford one, and 2)lure people who want a 911 but can't afford a new one and are afraid or unwilling to buy secondhand.
As it turned out, they made the Cayman handle a little too well, and people started opting for it not just because they can't afford a 911. When Porsche saw it was cannibalizing 911 sales, they turned the 911 into a bigger, more luxurious GT with a stratospheric price tag, and at the same time raised the price of the Cayman to about where a base 2WD Carrera was a few years earlier.
I prefer the last-generation 911 over the new one, or a Cayman, so that's what I drive and am biased toward. I also find the back seat imperative at times, so a true 2-seater doesn't fit my bill unfortunately.
If you go for a secondhand Cayman, make sure you get one with the 9A1 engine (from '09 or '10 IIRC, the 911's began it in '09), not the earlier M96/M97. The earlier engines have a horrible record for catastrophic failures on two counts. Google "Porsche Intermediate Shaft (or IMS) failure" and "Porsche Bore Scoring". The 9A1 engines do not have an IMS, and the cylinder sleeves and cooling jackets have been redesigned/improved.
Also a personal bias, I do not care for the PDK transmission. Yes they are quicker to shift either automatically or with the paddles than most anyone can do with a clutch and gearstick. But unless you are running it competitively on a track, or frequently in traffic jams, the old-school 3-pedal manual is a helluva lot more fun. These cars are cramped, noisy and rough-riding. If you want the comfort of an automatic, get a Lexus or Mercedes or Cadillac.
And whatever you do, my advice is to get a comprehensive "bumper to bumper" extended warranty. There's a lot of bloviating on the 'net about how those policies don't pay off and are designed to make money for the company, yada yada yada. I paid over 4 grand for a warranty on mine, and so far it's paid me more than double that back in covered repairs. And it's not that the car has been any more unreliable than average. It's that every little seemingly innocuous repair costs a staggering amount.