What do I listen for when buying gear?
When I listen to speakers I listen for balance. What I mean is how well the speaker excels at maintaining proper volume levels between low, mid and high frequencies. One of the things that turns me off from a speaker is if the bass is boomy and drowns out the midrange or the tweeter is to overpowering that you become agitated listening to the music. The frequencies should not be so overemphasized in any one range that the sound becomes unrealistic. If the speaker passes this test then I look for a good size soundstage. The sound should fill the room and not sound like it's coming from the speakers themselves, but from the area in between you and the speakers. It should sound convincing.... musical.
The benefits of getting better gear are subjective at best. Afterall, what is better gear? I have heard many people make comments or post reviews about how product x is ten times better then product y at a fourth of the price. I believe that the diminishing marginal returns you get in sound from extremely expensive gear is not worth the price you must pay. There are many reasonable priced pieces of equipment that will do the job as good or better and you don't have to take out a mortgage to buy them. Bottom line-- Don't assume that more expensive is better. It has to make sense.
It sounds to me that you have been somewhat unhappy with your present speakers or you wouldn't want to replace them. Maybe the speakers you currently have just don't sound right with rap music.
I am not a fan of rap music. I have heard it many times, but I just don't like it. I know that these rap music bands use expensive equipment to record their albums, but that makes absoultely no difference. Its the recording engineer that makes the difference. I find that rap music is deliberately recorded with overemphasis in the bass and mid frequencies. It is possible that your system is revealing these qualities within the music so ruthlessly that over time your brain becomes dissatisfied with the sound. (i.e out of balance.....not musical). Perhaps a less revealing speaker or one that is not so neutral may help.
Believe it or not the person who mentioned Cerwin Vega speakers is making a good recommendation for rap music.
You may also want to consider going with tube gear. It may take the edge off. I think tubes sound more musical. They create a convincing picture to me.
Whatever you decide to do I would re-think your next speaker purchase and maybe consider looking at your whole system with regard to the music you listen to. I would hate for you to go out and buy expensive speakers and still have the same problem.