Even a cheap system can sound good - since our brain gets used to our system after awhile. I enjoyed my sony-bose combination back in college immensely - I listened mostly to operas and I was so very happy, til I started listening to better gears, and found the law of diminishing return. The companies are charging us way too much in high end audio. A well chosen midfi can be profoundly satisfying as well.
If you are satisfied with the sound, go ahead and enjoy the music - that's what this is about, and not about components - we sometimes forget.
I would upgrade the speaker wire though. They made a difference even on a shelf system. I went to a hardware store and bought the thickest solid copper wire ($.49 per foot) intended for house electricity. It sounded pretty good by it self, but sounded even better when I added monster cable to it - combined both. The solid wire gives clarity and core to the sound, while the monster cable adds something nice to the sound.
If you are happy with your system, I would just enjoy the music, and consider your-self fortunate. There are some who dish out many-K dollars and still unhappy with their system.