I tend to agree with Perfectimage in that you should have a sense of what the final outcome is going to be and pick and choose as "deals" become available and your budget allows. That said, however, there is much to be said as to upgrading your souce components first and then working your way to the last link, i.e. the speakers. The old axiom "garbage-in, garbage-out" certainly applies in audio and what you hear coming from your speakers will reflect this.
What is your upgrade philosophy?
With at least 4 or 5 (perhaps as many as 7) components (plus cables) comprising the system at any given time, certainly one is the best at what it does and one is the worst, and the others in between. When you have the fever and spare cash, do you prefer to take the one weak link and vault it to the top of the pile, or would you for the same money upgrade perhaps 2 components to middling status? Seems the former yields a better system long term, but the latter would provide more immediate improvement. Is there a method to your madness?