I agree. The best upgrade you can give the bike is to finely maintain and rebuild as required. You'd be amazed at how well even baseline product can work if it's tuned and maintained right. Even cheap wheels roll like top end stuff when the bearings are cleaned, new balls installed and the preload is tuned to just the right setting.

On the other hand if you swap out stuff for higher end product but don't properly tune it then it could very easily end up not working as well as the stuff you took off.

Why not take this as a project for learning how to work on all the components of your bike.