[...] I'm starting to think that I am a bit too much of a stickler for details, spending 90% of my time on the 10% of things that probably don't matter, [...]
As others already said, it's the opposite, those 10% are what mater the most.
It's what show your implication into the story you're writing. It's what show the serious with which you're taking your role of author. It's what show the respect you have for the players.
For example, let's say I have a scene where two characters are walking and talking, does it ultimately matter if I just have only one render of two characters walking throughout their entire conversation of 10 lines of dialogue, or will it have made a noticeable difference if I had 10 renders of them actually walking while they spoke?
It totally depend of what they are saying, how they are walking, and how important is the scene.
In
The DeLuca Family, there's a scene between MC and Isabel, where for a long time the only thing we see is Isabel face, and the CGs change almost with each dialog line. It's important here, because she's telling MC to stop trying to have an affair with her, while in fact having an affair with him is all she want. Changing the CGs permit to show the internal conflict she have at this moment. She's saying something, while her expression show the opposite, with more or less intensity depending how big is the lie she's telling at that instant.
But would the scene be different, with her agreeing by example, less CGs could perfectly do it, because there would have less to "visually say". Two/three CGs, being her smiling more and more, to show how happy she is that MC love her, could have been enough.
Said otherwise, in Visual Novel there's "Visual", a part that shouldn't be forgotten ; the CGs should carry as much information than the dialogs. What mean that they should change each time there's a new information to provide. This being how VN should be done, the visual replacing the useless internal thoughts, and/or useless narration, thrown to the player face.
Go back to my previous example. The scene could have add an internal though between each dialog line, with Isabel thinking "I'm lying", "My god, why am I saying this while what I want is to kiss him ?", and so on. Instead it have Isabel face showing how much her thoughts are different from her words.
So, to come back to your example, the number of renders for this walk depend of the important of this walk and what is said during it.
If it's something important, change the CGs often, to depict the reaction(s) to what is said. If it's more on the filler side, two/three renders can perfectly to it ; yet more to show that they are effectively walking, more than for anything else.
In the end, all is a matter of importance.
Is the detail you want to show important for the story ? If yes, then you've to show it, always.
Is the detail you want to show important for the character's personality ? If yes, then show it, but don't abuse.
Is the detail you want to show important to put some life in the game ? If yes, then show it, but don't abuse.
For everything else, I'm tempted to say that the less you do it, the better it is. Not that it need to be totally removed, but too many games fail because they try to overdo it. They flood the game with purely useless detail, what tend to annoy the player on a long run.
- As previously stated, multiple renders for moving vehicles and people while mid conversation
- Random passerby's on a supposedly busy street or school campus
- Different appearances for those random passerby's unless they happen to be the same person from previous
Both fall on the living feeling. Show that the characters are effectively moving, and that there's a whole world behind. But don't abuse it, one CG every ~5 dialog line is generally enough.
- Decorations in a house (light switch, power outlets, pictures, coat rack, shoe rack, dish rack, knives and a stocked kitchen)
This fall more on the "useless details".
But everything is relative, especially here. The house need to feel like a living place, so it need to have some decorations, objects, and all. But there's no real need to constantly update this. No one will really complain because the knife rack is still full, while the MC is using a knife to cut something ; there other knifes in the kitchen, he use one of those.
But yeah, in the same time, if you left a magazine on the couch, remember to remove it at some time. It will not stay there for months, but no one will really notice if it stayed for three days in a row ; in fact, it's probably because it stayed for three days in a row, that player will notice that it isn't there anymore.
- City buildings, trees, fences, etc that block out the horizon line so it doesn't look nothing exists in a certain direction
Background life, that is needed ; the number of MCs who live in the middle of nowhere, while still being two blocks of everything is amazing. But it don't really need to evolve with time. What is different from the foreground of the city, that can possibly be optional (depending where and when), but have to change every time.
This being said, there's a moment when you'll reach the feasibility limit. You can't really have crowded streets, or background that change for every single CGs ; whatever if it's 2D or 3D, it would be too much works.
- Variety of food types at a cafeteria versus 1 or 2 types only
In display and showed, yes, available, no.
Do not ask what the player want, unless it's significant for the story, but don't make the player eat the same thing every single time. Yet, there's an exception here. The food can be part of a personal ritual, like him taking always taking his favorite sandwich every Friday, as a way to mark the break between the week and the week-end. But then try to make it explicit, with by example a friend saying that he always eat the same sandwich, and the MC explaining why.
- Gizmos, gadgets, chemicals, safety goggles, etc in a classroom laboratory
See what I said regarding the house. Except that here they need to be at their place. Make them be used when they have to be used, else they need to always be when they are stored.
- Matching furniture styles (An house with a modern design and feel should have modern-styled furniture instead of a traditional-styled sofa for example)
It totally depend.
Matching furniture are a luxury, most home have whatever the owner like and can afford. Plus, you can perfectly have a modern couch and a classical dresser, there's no real incompatibility here.
This apply especially when it's in different rooms, there's people who like to have a different feeling depending of the room. The kitchen is practical and modern, the bedroom more cozy and good looking, and so on.