I think it requires very little work in the code, and much will give for graphics.
Now we have new clouds from Soczkien, but this is only one texture
Much better will be
NEW-CLOUDSdry.tga
NEW-CLOUDSrain.tga
NEW-CLOUDShrain.tga
And of course changing these clouds depending on the weather
Good clouds do a lot for general graphics.