I think everyone here has mentioned already, it largely depends on what you want to do with it, but also what do you want to be doing in the future? Do you want the photos you're taking now to be a part of that future or (depending on your plans) are you willing to sacrifice all of these pictures to the ether as just practice shots. I'm in a similar situation myself, however, when spending a lot of time and money to go out on expeditions to film remote areas, I can't afford to spend the next year just practicing and throw away the shots I get because I didn't have the equipment to get the quality I'll eventually need. For the development of a feature film/documentary such as I'm working on, the noise performance, video and available glass from your current camera just wouldn't cut it, even daylight shooting with my current D3300 is a stretch.
Similarly as everyone has said above, glass is the most important part. Pick your platform, (whether your current camera or otherwise) based on the glass available to do the type of photography you want at the price point you can afford. Astrophotograpy - Wide angle and as fast as possible. Sports and wildlife - Telephoto w/ image stabilization and quick Autofocus. Portraiture - 50/85/105mm and as sharp and fast as your wallet will allow.
Check out Tony Northrup's What Camera Should I Buy video on YouTube.
From my own knowledge and research (Excluding Flagship $6000 1D and D5):
Astrophotography - Canon Full Frame
Landscapes (Exclusively) - Pentax K1
Landscapes + General Use - Nikon D5300, D500, or D810
Video - Panasonic GH4 or Sony A7R2
Video (Slo-Mo) - Sony RX10 II or RX100 IV
Sports and Wildlife - Nikon D500
Portraits - Nikon D810
Vlog - iPhone
That said, these are sort of the upper echelon of what to use to get the best possible results for specific applications. You can of course use any camera so long as you understand it and know how to compose shots and use light. What did the man say, "The best camera is the one you have with you." Similarly, as Mr. Northrup points out, if the quality of your gear is good enough for you, spend your money on going places to take photos rather than on gear.
For my own purposes, I will be getting the D500 to replace my D3300 as it seems to be the best all around camera, it has 4k video, and my current glass catalog is all Nikon. Will probably keep the 3300 around for timelapse though.
In summary, What do you want to do with your photography now and in the future? In your opinion, does the quality of your current setup achieve that goal? If yes, spend your money on trips or other gear such as motion control for timelapses. If not, figure out what setup will achieve that goal, and decide whether you can afford to take the time to learn on your current setup and transition later, or if you need to learn on something you eventually want to end up with.
