I can attest to bugs on the windows. When I road in the Cab of an SP Cab Forward in 1951 the engineer told me not to stick my face out the open windows (that was air conditioning in 1951), I had desert flies stuck to my teeth.
I think all of us make decisions regarding what makes things more realistic for us. When I was a three-rail “hi-railer” sometimes someone would point out my layout wasn’t as realistic as theirs, because their HO layout had two-rail (usually brass) track whereas mine had three. I would point out that I’ve never seen a power company plant power poles and then leave them empty like on their layouts, where my poles were all completely wired - even having wiring going to the buildings.
Some people make highly detailed models, then leave them pristine. I weather pretty much everything - engines, cars, buildings etc. - because to me that makes them more realistic.
On my diesels, I like to find one or two details that seem important to me, and add them. For example, M-St.L and NP diesels in the 1950’s often used ‘recycled’ steam engine bells, so my M-St.L RS-1 and NP RS-11 have those type of bells added. Otherwise, the models (Atlas) are basically stock. I’ll add a more accurate diesel horn if needed, although most early diesels just used the single chime ‘blat’ horns.
Having thought about this a bit more, I would say there are several things very important to me for realism.
The track arrangement must be realisitc. To me that means long and linear and not sharply curved or stumpy.
The proper type of loco should head the train.
Cars should have roadnames that are consistent with the area modeled and consistent with the industry receiving the spotting (I wouldn’t put a Clark Oil tank car in front of a Corn Syrup processor).
Model the common, not using the one off “there is a prototype for everything” excuse. As a free lancer, plausibility is everything.
Buildings need to be large enough. Land and lots on which the buildings reside need to be appropriate for the area modeled (more spread out in the suburbs, etc.)
Everything must be weathered, dulled down, muted colors like sun fading.
I’d have to say that way down the list of important things that add realism is the actual detail level or even accuracy of the models, within reason.
The track arrangement must be realistic. My layout will model basically two cities.I do not have room to model the connecting trackage, so I will not have long and linear trackage. It is a better option for me to not have the connecting track than to resort to short and stumpy.
The proper type of loco should head the train. This is also a must for me.
Freight cars should have roadnames that are consistent with the area modeled. Since I have become non-specific about the area I model, this is no longer important to me.
Freight cars should be consistent with the industry receiving the spotting. Yes, yes, yes. No oil tank cars in front of a Corn Syrup processor here either!
Model the common, not using the one off “there is a prototype for everything” excuse. I agree 100%. Model the world as it is perceived.
Buildings need to be large enough. I don’t do this. All my industries could not fill a forty foot boxcar in a month.
Everything must be weathered, dulled down, muted colors like sun fading. Yes, I apply at least a little weathering to everything. If not, it looks too toy-like for me.
The actual detail level or even accuracy of the models, within reason. I just need them to look good enough in photographs.