Every image has an optimal viewing distance where it can be best appreciated as a whole. The are some people who are obsessed with detail and will stick their noses in anything, but most of us don't. So if you blow your image up by a factor of something like 5 (to 90 from 17), then people will stand farther back to look at it, which negates some of the lost detail in the enlargement.
If you really need to keep detail in a very large image, you need to start big to begin with. Shooting with a large or medium format camera is best. With scanning, you can't really make it better than the original.
PS: good to hear Genuine Fractals is still around.
Dale