So how would you spend $500?Not like this. Last thing in the world I would ever do is ask a bunch of random strangers what to do with my money. Only slightly higher on the list is asking a bunch of random audiophiles how to make my system better.
But oh well, you did ask what I would do. So here it is. I would listen to what I have, seriously and deeply, a very long time. While doing this I would make little adjustments. Perfecting speaker placement. Tweaking toe to hear the stage go flat and wide or deep and focused as toe changes. Perfecting listening location. Moving wires around listening for changes as they are raised above the floor or routed away from other wires.
When not listening I would read, read, read. I would read reviews on everything I might want, paying special attention to listening impressions while almost completely ignoring technical specifications. (Speakers must be above 90dB/1w, MC above 0.3mV, or I pass. All the specs you need.) Read reviews, read user comments on sites like this.
At your stage of the game I would also be doing everything possible to hear as many different components as possible. Preferably at home but in reality mostly at retailers. I would never, ever, visit a retailer and spend any time listening without asking them to change something. Could you put that power cord in so I can hear it? What about that interconnect? Listen and remember and compare- so this is this what the reviews were talking about??
Technically this is not what I WOULD do. This is what I ACTUALLY DO. Except I no longer visit retailers, sort of beyond all that. Really good, essential almost, for getting beyond the novice stage.
Ultimately, the good news is, rest assured whatever you buy, if it really is better you will hear it, it will elevate your system, and you will be happy. The bad news is it takes a whole lot of work to find the components that really are better, and not just different. A lot of components will sound exciting, or dynamic, or whatever catches your attention. Then after a while instead of the good stuff you notice the flaws. This is the real skill in listening evaluations, learning to differentiate between what is new and exciting and what is correct.
It ain't easy. Its way harder than asking a bunch of random dudes what to do. But it does have one good thing going: it actually works.