Although both performance cars I think the Cayman the the Sti operate in very different segments of the 'sporty car' segment.
The Sti, has a wonderful rallying racing legacy and is an incredible 'bang for your buck' car. It's really an engineers car. A car where the engineers are able to use every trick they can think of to squeeze out performance. In some cases the technology overrides the driver meaning that the technology is basically doing things for you. To someone who likes high tech and speed above all else that's a great approach.
Sports cars to me are a very different animal. The goal of a sports cars is driver engagement. Meaning the car should form a tight feedback loop with the driver where the car communicates exactly what's going on and the car responds sharply and precisely to driver input, all the way up to (and beyond) the limits of the car. A sports car invites you to chase those limits due to the confidence it gives you that it will stay with you all the way to the edge.
In a certain sense, the overall performance is secondary to this oneness with the car. It's a driver's car. The Miata is a good example of how a wonderful driver's car can have fairly pedestrian performance. Driving a sports car is more about watching the tach and trying get another 200-300 RPMs on exit without actually caring about the actual speed of the car.
Technology cars typically have a lot of performance and wow factor and are promptly forgotten the moment a newer 'tricker' bit of technology comes out making them obsolete. Driver's cars hold appeal generations later even when their performance has long since been eclipsed (see air cooled 911 as an example).
There's not really a wrong or a right choice, they are just cars for different purposes and different types of fans of the automobile.