Spectrum Computing

for the zx spectrum. barring Border color

I guess the answer lies in: Are there any adventure solutions that rely on something in the graphics and not in the text? That would be the only time a text adventure would need graphics.

I have a vague memory of at least a few adventures that required you to spot something in the graphics, but there is no reason they had to require that. In the general case they clearly don't, as all the successful entirely text adventures prove.