First of all, if what you say about your bike is true I would stick with it. It sounds like you have a bike that you really like. Second, from my personal experience, smaller upgrades seem to be lost or forgotten about a lot sooner that one thinks. I have put in new bottom brackets thinking that this silky smooth model is going to really be the next big thing with my riding... and after about the 2nd ride I never give it a 2nd thought.

But, if there are some consumables like a RD that isn't shifting a crisp as a new one might, then a new RD might actually be warranted. With that said, maybe just go and do a maintenance rebuild i.e. cables and housing, new chain, lube everything.