If you don't have lots of funds for component upgrades, I would work on the finer points of tuning your system. Clean all contacts. Separate your cabling so its neat. Play around with component isolation. Put some maple under your pre and cd player for instance. Inexpensive maple butcher block can be found at Home Depot.
By doing these simple things you will learn more about your system than if you went out and bought a bunch of toys.
By doing these simple things you will learn more about your system than if you went out and bought a bunch of toys.