I have 83 at this counting. Contrary to what others believe, I don't think that is too much. I don't use all 83, but I do have a standard rotation of about 25 or so. The rest of my balls involve specific drillings, and specific surface preps for when I go to certain tournaments. My collection of older balls with their milder covers really helps on drier conditions.
Knowing how certain tournaments tend to prep their lanes before hand, I will have an advantage by knowing which area of my equipment to concentrate on and carry with me. It has worked well so far. I rarely miss cashing in some form.