I like the idea of maybe changing out saddle, pedals and tires (but wear the first set of tires out while you put in some miles), maybe grips; things that fine tune the fit/feel of the bike. Some nice accessories like good shoes, shorts, gloves, hydration pack etc to keep it comfortable on a ride. After that save up for a different bike, it's not worth changing out major components. Ride a lot and improving your skills on and off the bike (both riding and understanding the components and how to keep them in tune).