Most of the dislike for the boxster that I have seen comes from people's subjective opinions based mainly on their perception of what the car is, rather than what the car really is.
If you spend an extensive amount of time with one it becomes evident pretty quickly how excellent a car it is, how well it is engineered, and how it outdoes every car in its class by a long shot. Experienced track drivers will instantly know it is better balanced and does many things better than a 911.
A lot of people I have met seem to like the Cayman better, until I tell them that the Cayman is mostly a Bosxter coupe, at which point they say "oh" and have that dissapointed look on their face again. I hear terms like "cheap 911", "cheap Porsche", "girls porsche", etc., but I like said these are mostly opinions from people who have never driven or understood the car. I've tried to guide people in the direction of a Boxster or Cayman many times and instead they have chosen to blow their budget and get a base 911 because it is more "macho" in their eyes, yet clearly the worse car for them especially with their driving skill level.
I think this may be one reason Porsche continues to keep around a car with an ill engine placement design like the 911. It is why it continues to hold down the power on the Boxster and Cayman so as to not upset the carefuly crafted image of its 911.
As good at people think the GT-3 is... I can assure you that a Cayman with similar power levels and brakes would leave it in the dust and be more of a joy to drive.
Personally I would take the "baby", the "girly", the "cheap", the "anemic" porsche over the 911 any day and put the money saved into more apropriate mods. If I tracked, I would take a Cayman and if it was a daily, I would take the Boxster S who... with the top off, is just pure joy to drive.
The Boxster suffers from some of the same image problems as a Miata... another REAL sports car that takes a beating because it's small, girly, wimpy, cheap, etc. People that make fun of these cars aren't really knowledgable drivers IMO. If one is, you have to give credit where it's due... to the outstanding engineering, performance, and value of these cars. The Boxster IMO, is and has always been a terrific car and a phenomenal value. Lots of performance, LOTS of room with two "trunks", great all weather capability with good tires (heavy drive wheel weight bias), and open weather in the summer. It has excellent steering, excellent brakes, good acceleration, is extremely communicative, is well balanced, and has terrific seats. Reliable and cheap on the used market. One of the best daily's you can own.