I nejoyed sound of ES110, but sound of FP-10 wasn't a deal breaker for me either... speakers could be better, but on the other hand I will probably play with headphones mostly anyway.
Hiya. Do try the FP-30 just to see what it possible with the built-in speakers (they're surprisingly good for the price).
I would also compare headphone quality/volume - due to the different speaker setup, there may be differences in headphone amplification on the FP10/30.
I know that on the FP-30, headphone volume can be low if using cheaper/less sensitive headphones. Perhaps take your own and try them out just to make sure that they work as you intend, else you might find the cost goes up if you have to get a different set.
I've never tried the ES110 myself - a salesman played it to me, the main piano sound was warmer and there were some lovely electric piano sounds too. It was my first ever piano purchase, so I based my decision on price as I had no idea how far I'd get with lessons.
In the end, I had the FP-30 for a year before selling it to get something with a better & lighter action... it was fine up until exam time where I increased the amount of practice - I then found that my finger tips started to hurt a bit. It's not been an issue since replacing it with something else. That doesn't mean that your experience will be the same - perhaps it was peculiar to my fingers.
I'd have kept my first piano for longer, provided that the action didn't cause me the same issue. It all depends on how long you've been playing and what you're used to I suppose.