Personally I am kinda more worried about all the graphics fitting together in a consistent style then I am making them all extra unique. Unless that style is purposefully a mishmash, but at least that is consistently inconsistent. Though part of me kinda likes the idea of going ultra minimalist like in this screen shot I have shown off before of a RPG Maker game I found:
I would probobly not go to quite that level of abstraction if I did it, maybe something more like Nethack's tiles:
For now though I am just using the VX Ace RTP and some similar style graphics I found online. Maybe a bit boring but it works.