It doesn't work like that (if I understood you correctly). Vital Spirit causes you to meet more higher levelled Pokemon in any given area, but their levels will only be as high as they naturally are.
E.g. I'm on Route 2 in Unova in BW, and I lead with a Vital Spirit Lillipup at level 15, but the Pokemon there only go up to level 7. I won't meet any Pokemon higher than level 7, but I will meet more Pokemon at that level than I usually would, due to Vital Spirit.
You'll only meet level 90+ Pokemon if you're at a place that originally has level 90+ Pokemon in the wild.