I can't say that I would expect hip hop to benefit from great speakers, but I did notice that the large amount of techno that I listen to did benefit from a well controlled speaker. Techno/electronica tends to use a lot of midrange and a LOT of stereo splitting/panning, as well as a lot of bass activity. I've heard quite a few speakers that don't do electronica well, and not so many that can handle it really well.
You are right, within your budget, you need to find a good balance between power and speaker, but that starts by choosing the right speaker for your needs, then find the right gear to power those speakers. Do that right and you can get away with any sub until you are ready to get a good one. There are a few subs that are quite good at the $400-500 point that will do well enough, which is why I say don't worry so much about the sub, or at least not a higher end sub unless you are looking for serious bass.