There's a lot of confusion in here. If tilesets and sprites' being limited to 256 colors meant that 32-bit color wouldn't be any different, then surely 16-bit color wouldn't be any different either? And yet clearly it is. 32-bit color would allow for better results when two colors are blended together (e.g. textured backgrounds, ambient lighting, translucent tiles) and even finer differences between colors within the palettes themselves. 16-bit color can't show you the difference between #010101 and #020202, but 8-bit can, and so could 32-bit.

None of that's to say it's an easy problem to solve on the technical side of things, but it's false to say there'd be no point.