I will answer with my opinion and respect to your opinion:
1. I don't think, that windows are so important in photo mode. if somebody doesn't wants spoiler\vents to replace windows, just use the original version.
2. ;) but have you tried ever in real life to wind the windows down at 200km\h ;) and it doesn't have to be air brake, it just can be spoiler, and the driver can pull it down when driving fast.
4. well i can live with that, i usually skip the scene, it gets annoying after a while. (also the moment when you wind your windows down, its a close up view, nobody can see the spoiler\vent)
5. thats why there will be 2 versions. for that mod you have to move and rotate 2 dummies, rename the parts, export, replace. it can be done for 10minutes.
6. i don't know, but for me the modding is to make people happy :) otherwise i will make the mods myself and use them privately.
7. most cars in the real world can raise their vents, spoiler by button, even when they are standing still.
8. i don't think windows have must have function either. yes, they change the interior sound, but there are people, who can live with that. :) this is arcade (hybrid) game after all, nobody should pay so much attention to the realism.
also the vinyls, other small stuff are also for the looks, but everybody likes them :)
9. yes, they are winded up. i don't see a problem...
10. yes, but like i said above, there are people, who can live with that.
11. different people, different wishes... when i play the game, i like to drive, not to wind the windows up and down all the time. (also when the mod is for spoiler, you can use the one dummy to wind the driver window, and the other for the spoiler)
12. its not a tough job, just attach the window to the door. also i just wanna ask, why don't try with one version, and let the people choose :D
13. yes, you're right, but i don't usually spent 15 hours in the showroom\house, opening doors all the time. once again, there will be 2 versions.
when somebody wants openable windows, download version 1. when somebody wants to drive with vents\spoiler, will download version 2.
i really don't see a problem to make everybody happy. :) (i'm not making a request, suggestion, i'm stating my opinion.)
Nothing personal, cheers!
p.s. also i think open-able engine bay lid would be more important (to see the engine), than to open the doors and see the interior (which has camera for it)
maybe it will be better to made high poly engines, and people could look at them. after all we should be petrol heads :D when i see super car in real life i want to see the engine. it makes more sense in a game, designed for car detail. also it would be cooler in photo mode. but i'm going heavy off topic, have i :D
in the end i'm making suggestions, which can make the game more detailed and cooler....