Just out of curiosity (like I said, I'm still relatively new to this), why not throw $500-600 at a $400 bike which is a year old?

It seems to me that upgrading a cheaper existing bike would be more cost efficient than buying another bike, and you'd be getting exactly what you want. You could also potentially have more money left over to save for a full suspension down the road. I realize the derailleurs and shifters are going to be higher quality on a more expensive bike, but dollar for dollar upgrades seem like a better bang for your buck, especially when you're talking about what is essentially the same frame. When the stock components start wearing out, replace them with better stuff.