There are many things to consider here. The first one is texture compression. The compression system that DTG uses is terrible. They use RGB565 which means the texture is compressed from 8 bits red,green and blue, down to 5 bits red, 6 bits green, 5 bits blue. This reduces the amount of bits used to store each part of the texture. For a "mixed" texture like grass or rocks, this isn't noticeable. But for textures where "pure" colours are used, like the red stripes in the Suwex version, or the blue stripes in the Dutch trains, the colour compression results in blocky square artifacts both inside the stripes and along the edges. This is unacceptable for almost everyone. I used to do my textures so they could be compressed, but the universal feedback I received in 2012 and 2013 was "this looks terrible". So now I suffix my textures with "_nm" which prevents them from being colour-compressed. That's a deliberate move on my part.
The second issue is shared textures. You'll find on most of my trains that parts of the train that are shared with other trains also share the textures. Normally this is things like bogies, wheels, electrical parts etc. Sometimes - as you've seen - things like the wipers get through. That IS something I can look at changing.
On, the memory issue. There is a lot of misinformation on how models are loaded into memory in this game. There is a perception that activating a particular author's set of assets when making a scenario, forces them all to be loaded into memory. This is not the case. If you build a scenario and activate "christrains" but don't use any of my stuff in the scenario, none of it it loaded. The same is true for multiple colour schemes. Unless a texture is shared (like the wiper that you pointed out), the other versions are not loaded unless they are used in the scenario.
There is also some misunderstanding about how texture memory is packed on PC graphics cards. A lot of people say "why don't you use more smaller textures for the parts like wipers and pantographs?". I could but I try to minimize the number of different textures used in any model. This is because of something called "state change". PC Graphics cards are very bad when it comes to swapping shaders in memory. For example if I can draw the entire train in one single large texture, the game will run faster than if I break it into 30 smaller textures. The reason is that each time the graphics cards encounters a change of texture, it has to "state change" and unload the shader that it WAS using, load the NEW shader and start drawing again. Each change costs a measurable amount of time. 10,000 triangles in a train with one texture will draw quicker than 5,000 triangles in a train that uses 30 textures.
So there are reasons why I make the choices i make. I can slow the game down and make the textures look really bad, but I choose to try to keep the framerate as good as I can whilst making the trains look as nice as possible.
The attached picture shows an example zoomed-in section an uncompressed texture (on the left) and what 565 compression does to it in the game. You can see also the slight 'blue' in the white colour has become more 'yellow' because of the colour-shift caused by going from 8-8-8 to 5-6-5. You might 