Replace the texture's of the HUD, update font quality, improve the fog and this isn't a texture but I would like to add a scroll feature (which I have no clue how I'm going to do this).
That resolution mod mentioned below is about all you'll be able to make do with the game. Any other "beauty or update enhancements" will either require a lot of work or some you can't do since its hard coded into the game.
What instead of replacing it, I just use an overlay?