I'd say that it should be optional and that we can easily generate a stripped resource file with spasm. Also 4 level is a bit different from 3. We should keep 3 though because it won't require different sprite sets for b/w.

I thought programming wise, there was no difference between 3 and 4 level gray.

Well it is different. In both case you have two bits (not learning you anything, if you want 3 or 4 values, you need 2 bits) for each pixel (so two buffers).

-In 3 lvl "mode", you basically have a black buffer and a grey buffer. Any "pixel" on the black buffer will be black on screen, and any "pixel" on the grey buffer will be grey on screen (except if it is black on the black buffer). Both buffers are quite independent, you can for example scroll the grey buffer without the black buffer having change in any way, so the grey moved on screen and the black stayed where it was, or the contrary, move something black without touching the grey.

-In 4 lvl "mode", that is different, because then with two bits you have exactly enough bits to make 4 numbers (so 4 shades). You now have a light grey buffer and a dark grey buffer. So you guess how to make white, light grey and dark grey. But then you have a problem with black: black is basically light_grey+dark_grey. So moving a buffer will move the shade of grey it is associated to, but it will also have an effect on black.

(at least, that is how it works in Axe, except if I am mistaken and if I made all my grey by luck in my programs).

A problem with choices for grey/not grey is the lack of space. Greyscale sprites don't look so good when you just use them as B/W sprites, so odds are you'll need a whole new set of sprites for each option.

If it's an option, it should be a different version to download. That way, the extra data won't be there (one of the bigger issues for BE models anyway)