My system sounds absolutely great as it is, but I am always looking for better sound. I am just not sure I will get it at this price point. Powered speakers (or studio monitors) are what I want the most as I want to save space, but if bookshelves are the better option, I will go with that. Here are the questions I have regarding my current setup and possible new setup.
At this point, along with the choices, ends up being a heap of subjectivity basically depending on who you ask.
For an actual upgrade, I would think the next step would be a listening habit upgrade other than just essentially swapping out other budget components for what you already have. Subwoofer, sure, but that's about all I could see as an improvement or, at least something new to play with for awhile.
I did desktop systems for awhile in about the middle or later part of my audio hobby but my next obvious upgrade was a large system again for a critical listening opportunity with a lot more options. I still dabble in desktop, or near field systems but I tend to treat those more as a convenient novelty than I do my main system.
All of those types of speakers you mentioned, I would end up getting used to and forgetting what my actual upgrade was from memory unless I had replaced something that was worn out or sucky to begin with.
ETA: I do own the JBL 305's and I had fun with them at home for awhile but now I have them at work and they do a pretty good job in my comparatively large shop space and I do like those speakers. But then, I am a long time JBL fan so. . . .