Roland HP-504 has the same technology as Roland FP-30, but in the cabinet style and likely better speakers.
So it is on par with ES-110 in technological aspects, but better as a piece of furniture. This piece of furniture style will cost you 500-800 more in a new piano. You can buy whichever you like more, but if you look for more advanced sound engine, you will need to shell more for higher models.
I think the PHA4 premium is like PHA4 standard with with also longer pivot and better key coating. So its basically FP30 technology with better key mechanics/feel.
So, most of the advantages of HP-504 are not that big of a selling point for me:
-Don't care that much for the furniture style cabinet. Just want something steady enough. I think the wooden stand of ES110 would be good enough.
-Bigger Speakers is also not much of a selling point. Will get a lot better sound with monitor speakers connected.
-Dont care much for coating of keys
-Technology was impressive when it came out, but it is now part of the lower line models. Even if the sound of the engine is better, I have lots of sample libraries.
-Dont care much about the input. My soundcard has 8 inputs/outputs. I can even make a surround sound speaker setup.
So, the only question really, is if having a larger pivot is reason enough to take my chances on a 6 year old digital piano that may break after a few years. If it was similar to the difference between ES110 and VPC-1, then I would definately consider buying it.