- Like what you've got: sorry, but it's time to move on. You really don't know what you've been missing. Bodies are better, sensors are better, everything is better.
- Dislike what you've got: if you like Fujifilm color, you don't have a lot of choices. The best choice would be to go mirrorless and get an X-Pro2, X-T10, or X-T1, but that means new lenses and flash units, too. If you want to stick with the F-mount you have to move to a Nikon DSLR or buy a used Fujifilm DSLR. The only used Fujifilm I'd even consider is the S5 Pro, as you'll have a hard time getting older ones repaired.
Some might say the their S3 Pro still has some legs left to it. A D3300 will out focus it, out write it, and has a better sensor, in my opinion. State of the art has moved on. Considerably on. Digital parts for the older Fujifilm DSLRs are getting hard to find (though the non-digital stuff is mostly N80, and there's a lot of N80's to cannibalize out there).