I've been thinking about this since the PS4 launched and we have gotten a few remasters. People are crazy if think these games wouldn't benefit from a remaster.
An overall higher resolution would benefit any game, so that's a given. And while some of the textures were upped for the PS3 port of the first game, it definitely wasn't all of them. There are quite a few textures that were a little lacking. Framerate was good, but i'm sure there were a few dips here or there. They could increase it to 60 fps, or have it unlocked and hover around 40-45 fps, like Infamous:SS (that game was buttery smooth.) And since this game takes place around a lot of water, more realistic water would be nice. Of course, the biggest improvement for any game, especially those that have a great (sometimes creepy) atmosphere, is better lighting and AA.
The same really applies to all 3. A remaster of these games would be breathtaking.