I agree with some of the points above that the synergy of the room has a huge effect on the quality of your listening experience. Over the years I have made numerous improvements and I am currently content with my system. I frequently visit retail stores, high-end club meetings, and as many high-end setups as I can and I keep trying to find one that sounds better than mine and I can't. My system is relatively modest compared to some of the systems I listen to, but for me it works. I get almost equal gratification from knowing that I bought every piece I own as lightly used, second hand equipment - and for me, that makes it sounds even better.
I suppose I may upgrade something at some point down the road, but at this point I am 100% happy with my system and I love listening to it.