I think this is a perfectly good approach, as long as each sprite aligns properly with each other.
3x3 sprites suggests you can travel both horizontally and vertically I guess?
And by using sprites, I assume you have prerendered textures to switch between?
Are they all the same texture? (just positioned differently so that you can move and zoom in/out)
In any case, I’d like to highlight the possibility to use a screen space quad, that always
fills the screen perfectly. I don’t have a small example for you, but perhaps others can help here. Found this example.
You can use the shader to zoom in/out by scaling the uv coordinates. By doing so you can also produce multiple layers in the same quad by sampling the texture several times per pixel, each time with a scaled uv coordinate.
Anyways, just thought I should mention it. (Sounds like a fun task for someone to help experiment with 
)