Database with suggested settings for every playable game

That is what the wiki is meant to do for each game, as in this example.  However, it is still not well populated yet.  This is no doubt, a labor of love from a few people and I'm sure it is hard to keep up with what works on each game when the emulator is constantly evolving.  
Eventually, default safe settings for each game could be handled with a robust ini file system like Dolphin has, where the emulator ships with default ini's for each game, and there is another layer of user ini's that can be used to overwrite or add your own settings.