Disclaimer : I know this topic is 5 years old, but my post could be useful for anybody who want to extract ressources of this game.
The SPR files are indeed uncompressed 8 bit (256 colors) data.
However there is a header : first byte is the number of sprites in the SPR files. Then it is followed by byte pairs (as many as the number of sprites). Each pair describe the width and height of each sprite.
03 20 10 15 30 70 80
We have 3 sprites. First one is 32x16 (0x20 0x10), second one 21x48 (0x15 0x30), third one 112x128 (0x70 0x80).
After that header, is the uncompressed pixel data. Each pixel is one byte.
The pixel data is not stored in a linear (chunky) fashion. Rather, they are grouped into 4 planes. I think it is like that is because the game use Mode X. By storing the data that way, the game can flush data directly into video memory as it is in the file without any conversion.
Eg : how pixel data is stored in the SPR file
How it will be shown on the screen
Trivia : the appearance of the customers you meet in the game is randomly generated. To generate a new character, the game randomly select a human body (from skinny to fat), then add a pant, shirt, accessories, etc...
Funny fact : those guys are actually naked under their clothes
(you can even see pubic hairs for one of them)