OK let me answer to those in the same manner you asked them.
1: GTA V WILL have better graphics than GTA IV.
2: Whatever power the 720 might possess, the gameplay will be more or less the same on all the platforms. So don't think that you can get special features on other platforms. And this fact is true to almost all cross platform games.
3: We PC gamers can do nothing BUT hope that Rockstar games have learnt from their mistakes.
4: GTA V will be way better than GTA IV and it might be better than San Andreas. (San Andreas was a great game, so GTA V will have much to do to trump SA).
5: After typing all that, my head feels a bit too light to think about that. LOL.