Now how about detail texturing? Even at 4x the size many of those images still seem a bit blurry. Detail texturing would greatly help everything to look sharp, especially up close, and would also be very, very practical.
For example, how many N64 game have grass textures? create a detail texture for grass, and then that will work for every game with a grass texture. Same goes for dirt, rock, and stone. For more complex textures you may have to create a detail texture for it only to get the best lookng effect, but most textures could be reused.
Why not create one big detail texture pack which is compatible with as many roms as possible, link each detail texture to a texture in each game using a definition file or something similar?
The great thing about detail texturing is that it can be tuned to meet computers of different capabilities. For example, a slower computer wouldnt render the detail texture as far, while a faster computer would have a larger draw distance.