“Don’t imagine Gregor, Don’t Imagine Gregor, DON’T Imagine Gregor, STOP IMAGINING GREGOR!!… Don’t allow the imagery to do it’s desired job. Don’t let Kafka’s Metamorphosis make you cry..or throw up. Look beyond the cockro.. 
A FEW MINUTES LATER…
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Gregor was a shell of a man before he transformed into a bug
Okay, I’m better. Time to explore, decipher, discover, and unravel the true nature of Kafka’s characters. The main cockroach, I mean, character Gregor. He’s a traveling salesman, he supports his family, he’s alone, so alone. Unlike myself, he lives his life logically, robotically, and selflessly. He definitely unintentionally fell into his pre-cockroach lifestyle. I feel sorry for him; I want to spark some emotion, some fire into his life. I want him to smile just to smile, laugh just to feel the tickles in his stomach. But sadly I can’t change the story, can’t ignite any feelings into an already designed and printed character.
Through out the story I waited for Gregor to “grow a backbone” to do something for himself. To metaphorically take a stand and change his fate, maybe than he would’ve been able to change back into a real man. 
But despite my wishful efforts, Gregor remained stagnate. He became what the mirror reflected; dying a man stuck in a hard shell. Dying for the family who never appreciated him nor his contributions.
While Gregor failed to excite or inspire me, Grete, his ever-changing sister, grasped my attention with her first mention. She brought life to the short-story as well as an over-whelming sense of development. Albeit, Gregor was the man who physically transforms, Grete is the character who truly sprouts as the story progresses. 
Starting Metamorphosis as but a child in my mind, Grete ends the story as a beautiful woman who is still growing and stretching. She is the only family member who cares for Gregor, who feebly tries to turn him back into the brother who once loved and provided for her. However, upon maturing and realizing that Gregor is never going to be the same, she deducts that the cockroach which occupies her brother’s room must be disposed of. With that, gone away is Gregor’s last attachment to the world, and to the other world he goes; proving his only purpose in life was his family.
The mother and father are nameless because they don’t deserve any more attention then they are already given. They are dispensable characters that Kafka includes for fluff and drama. Emotionless just like their cockroach son, they are empty of any sympathy and blind to any outside concerns, Gregor’s parents are, in short, just another reminder how alone Gregor is in his robotic world.
The manager is a selfish coward, the maid-lady a freak; and the three men ambiguous characters that I just don’t get. The other characters I purposely forgot to think about, sorry..not sorry.
I really like your view of Grete as a blossoming young woman (to paraphrase). There’s this sense that, by the end of the novel, the story’s protagonist was never Gregor–in fact, he stays static in personality and mindset throughout the entirety of the novella, instead inspiring changes in those surrounding him.
However, I actually viewed Gregor’s parents a little differently: they don’t seem to be included for fluff and drama to me, but as dependents who become independent as a result of Gregor’s disabling. It’s almost as if they’re his children rather than he being their son, and they must stand up and become adults once he is unable to care for them.
And focusing on the Samsa parents’ lack of names, perhaps there is that lack because the focus of the reader needs to be on Grete, as the protagonist of the story? You brought up a very interesting point when you said she grasped your attention with her first mention, and maybe that’s what Kafka was going for all along by only naming Gregor and Grete.
I completely agree with your opinions on Grete’s transformation. While Gregor seems to be the most obvious main character, one could make the argument that it is not Greger, but Grete who Kafka intended for us to focus our attention on. For the most part, the characters stay static throughout the course of the story. But not Grete. While everyone is so focused on Gregor, Grete undergoes a transformation from a child into a beautiful young woman. However, this transformation is only apparent once Gregor is gone and his family, as well as the reader, finally has a chance to relax without the stress of him pulling us down.
I also thought that while I don’t 100% agree with your interpretation of Gregor’s parents, I still thought that was a very interesting point. I viewed his parents as a crucial part to the story since it was them who I believe influenced much of Grete’s opinions.
I also want to point out that with Grete’s transformation into “womanhood,” she also loses some of her patience and humanity. While she does seem somewhat sad following Gregor’s death, Grete also has a moment of anger towards Gregor when she verbalizes her wishes for him to leave the family. I can’t help but to hate the new Grete and I think that if Gregor had lived, Grete would have actually changed for the better. She would have learned to become a sympathetic and kind caretaker, and instead of being prepared to become a housewife by her parents, she would have gone to the conservatory and created a career for herself. Basically, I hated the entire Samsa family.