Well... there is a case for remastering being done to visually improve the overall appearance of the game; in some cases to improve upon assets that were limited for the target system specs of the game.
Homeworld and Die By The Sword are good example, because the originals shipped with crude 3D models, and software renderers. With the advent popularity of dedicated GPU systems, the games could get an updated look that makes good use of the expanded features of the new platform.
Fallout was at one point considered and researched to use polygonal 3D assets, but they couldn't get the performance they needed out of the target machines; but imagine now if they could re-release it using the original 3D assets (or closely derived) instead of rendered sprite copies. The figures, the talking heads, everything could then take advantage of dynamic lighting and animation.
Think about an Obsidian remastered Fallout 1 & 2 done like this:
Krome Studios did a top-notch remastering of the Bard's Tale Trilogy; in Unity 3D.
Microsoft/Bungie did the same for Halo Combat Evolved:
What I didn't like about the Homeworld remaster, was that they tampered with the gameplay; (that's a no no IMO) but visually it looks superb. The voice work didn't really need to be redone, and they did not surpass it.