What's so good with having to upgrade the components of your bicycle is that that item that you'll be replacing won't be wasted. You can still sell it to lessen your expenses on the new item that you'll be purchasing.
This is what I have been doing whenever I have to replace or upgrade some components of my bicycle. The good thing is that I am so lucky to be able to sell them right away to some friends who would be starting with biking.
This is probably what most riders are doing whenever they are upgrading some components of their bikes but for a few, they try to keep the old components to build a new rig. This behaviour is sometimes termed as "upgraditis" to sound like a disease.
There are times when I am already admitting that I have this disease because I can't resist to upgrade my bike's components everytime I visit a bicycle store. So to prevent me from worsening my so called disease, I try my best not to visit these bicycle stores so that I won't have the urge to purchase something. I think I need a rehab. :-)