I play on CRT too, I use genplus-gx and retroarch. Is funny because I started to do the same thing as you when I read this from the genplus doc:
https://genplus-gx.googlecode.com/svn/docs/genplus_manual.doc
"VI Trap Filter let you enable/disable Video Encoder output filtering. This filter is usually implemented on modern consoles to improve color separation in the “low quality” Composite Video signal and therefore might not have any effect when using S-VIDEO, RGB or Component cables.On older consoles like the Genesis, this property of composite video was used by game developers to create additional “fake” colors on screen and various effects (shade, transparency). By disabling the filter, you can somehow recreate these effects as they were intended to be displayed (but still not exactly since the Wii still outputs a cleaner video signal than your old Genesis).
This option is only available on Wii."
"NTSC Filter let you enable/disable NTSC software filtering. This filter emulates the native artifacts produced by the NTSC Video Signal (color blending…). Some games indeed use this effect to simulate additional colors or transparency effects. Please note that this filter is very CPU consuming. Several predefined modes are available (COMPOSITE, S-VIDEO & RGB) which simulates a specific video signal type."
The only one I found for snes is the VI trap filter on retroarch. I suppose it will be impossible to get the same effect for snes if retroarch don't inplement the same composite filter for snes, since as mentioned above, the wii still outputs a cleaner video than the snes or genesis as I understand, using composite cables or not.
I would love if I can get the same filter for the snes core on retroarch, but it says that is very cpu consuming, so I don't know how that would affect snes games on retroarch, so yeah, to get that retro-feeling, you need to "force" worse composite quality with the filter.
So the only thing we can do, is disable VI trap filter, that will be for the moment the closest thing to achieve similar image to a original snes.
Is funny that I want this, and then I see retro-gamers modding their old consoles to get a cleaner video.