One of the lame parts of TLOZ was the shoehorning of a romance into an episode to fill time. Season 3 had lots of that pointless romance with characters we knew we would never see again. Chekov and Irina, Spock and Droxine, McCoy and Natira, Chekov and Sylvia from Spectre. The thing with Scotty was so sad. In Adonais we see Scotty hovering over Carolyn and in the very teaser McCoy comments that it appears that Carolyn isn't really into him! So In both cases Scotty seems to be a lot more into the girl than vice-versa. That weakens his character more than it helps. And I also hated Mira's attitude and general nervousness. I think her character is a worse statement on women in Starfleet than Janice Lester. Lester's comments can be attributed to someone who is a homicidal nut-job. Maybe women aren't really as discriminated as much as she states because she wants to blame someone rather than herself. Mira genuinely seems to be in over her head on the ship and comes off as immature.
The scary aspects of Zetar are good. The creepy Zetar voice, the dark Memory Alpha base with the dead people, the weird voice coming from the Tech, the disconcerting viewer image of the "cloud" returning to the station. I wish they had added more scary, weird imagery and cut the romance entirely and the whole quasi "court-room" discussion of Mira.
As a Star Trek romance, TLOZ isn't for everyone. Even though I strongly disagree with you on several points, I nevertheless respect that you have your own opinion. We all do. I'm sure there are "Turnabout Intruder" and "Plato's Stepchildren" fans out there somewhere, and they must have their own reasons for loving these episodes.
Romance isn't everyone's thing, obviously, and that seems to be especially true in the world of ST. Re: Carolyn Palamas, she was polite to Scotty, but that was all. She never had the same level of interest in him that he did in her. Even McCoy saw that. It happens, so we live and learn and move on. Mira Romaine, however, is an entirely different story. She is beautiful, highly intelligent, sexually attractive, sweet, kind and very much a woman of substance which is fitting because our beloved Chief Engineer is very much a man of substance. And yes, they are both very much attracted to one another and also very much in love. Scotty and Mira represent a May-December romance in its most beautiful form. I don't want to take up too much space in this reply, but I invite you to visit my blog for an in-depth discussion of this episode which will hopefully shed some light on the characters and plot. I will, however, address two points.
As for Mira's attitude, we need to keep several things in mind. It is while she is on her first assignment for the Federation that she and Montgomery Scott meet and fall in love. It wasn't something either of them anticipated or planned on--it just happened. Mira naturally wanted to do well on her first assignment and she was until the Zetar's first attack on the ship. Embarrassed at being the only person out of 430 who passed out, she simply wanted the ordeal to be over with so she could return to duty. She was fearful of saying something that could jeopardize her assignment (new jobs are stressful enough as it is), and this is why she appeared to be uncooperative and answered McCoy rather sharply. It's not out of malice, dislike or disrespect for the doctor, but just out of embarrassment, frustration and a silent but growing fear of the strange, terrifying thoughts and images that are beginning to take over her mind. She tries to listen to what Scotty is telling her about the effect that deep space travel can have on people, but deep down she fears it's far more serious than space sickness. Let's recap: falling very much in love while on one's first Federation assignment AND attempted alien possession nearly resulting in death. Seems to me that's a helluva lot to have going on in your life all at the same time. How well would any one of us handle that emotional overload?
Lastly, many people criticize poor Scotty for his actions in this episode. He's deeply in love with Mira (which I think is just beautiful), so how do people expect him to act? Say to her, "Gee Mira, I hope everything works out okay for you. If you live, let's go have dinner and shag tonight, okay?"
Really? 
Speaking from the female perspective, Montgomery Scott is worth his weight in gold (as well as dilithium crystals), and what woman wouldn't want a man who is that much in love with her?

Just my humble thoughts.....