Good call, but it does violence to the ASCII creature:-(
That's why I suggested gqip on every paragraph, but I'm sure there are more efficient ways.
Could you place the cursor just above the ASCII art and then wrap from there to the top of the document?
For that, you could place the cursor above the ASCII art; press (ma) to set marker 'a'; (gg) to go to the top; (gq`a) to wrap until marker a. ;)
Ah, I do see your point!
gqG also does violence to some plain-text formatting, such as numbered lists or other short sections in which a specified line length or presentation is preferred.
Long lines and wrapping within the text viewer is probably your best bet.
Why three g's at the beginning?
(g) invokes extra commands. here two are used: (gg) places the cursor at the top. (gq) wraps the text until (G) the end of the document.