I have a HD800S so I'll say that yes, it's worth it, but I'm biased.

First rule for any hobby : if you don't have that amount to spare or if you depend on it for living, don't spend it. These things come well after the rest.

And tbh if the rest of your chain isn't already good or great then the HD800S will feel like a wasted jewel among trash, it reveals all the flaws in your system