Good work so far, it looks pretty complex.
I'm thinking there are ways these textures could be optimized. Unfortunately that's something that's better off the closer you implement it at the planning stages. Hope is not lost here, there are other things you should do if you can help it.
Thoughts:
Have you nailed down the lighting? That might be the biggest issue here. Is it foggy and overcast, etc. If it is, then you could up the texture definition more because all that light is diffuse, top down, and mostly doesn't change. It does push your texture skills, even more if you are deciding what to reuse/tile and where, which you can do more of.
Added vertex lighting if it can handle that for the shadows. It looks like Phantasy Star in the
link used quite a bit, and the lighting and textures are more consistent than what you have so far. Similar restrictions, but actually they are just optimizing for what your eye prioritizes.
And with this sort of vertex lighting it can still double as a night scene, without redoing every texture for lighting differences. But if you wanna redo every texture for that anyway, reach for the sky dude. It's a portfolio, more is more
Lighting ideas:
Paintover of image 6 from reply #4. Yeah, very muddy stuff, but also done with the limitations of vertex painting in mind...
Digging into (no pun) what devs did working under such insane restrictions (from today's view) can be fascinating stuff. I think it will pay off. I'd like to get into more low poly myself, so probably the above crit helps both of us. Hope that wasn't too much of a ramble and that it helps.