The key to bringing out the full potential of every instrument begins with the set-up. Every detail matters from the size of the bridge to the diameter of the sound post, to the string spacing at the top of the bridge and at the nut. Even the curvature of the fingerboard and distance from the tailpiece to the bridge matters.
Unfortunatley cracks do happen, but it is very important to have them properly reapired to help maintain the instrument's value.
I only use the highest quality Mongolian hair that I can find. I have three different blends of hair: White, Brown, and Black, all of which are grade "A" hair. I also the hair in combonation of each other, most commonly black and white (salt and pepper) or brown and white (cinnamon and sugar).
Just like instruments, bows also suffer from normal wear and tear use. When the headplate becomes cracked, it no longer offers the same protection to the stick as with a fully entact headplate. Does the screw no longer tighten the hair, then you may have a stripped eyelet. Eyelets do wear out over time and will need to be replaced with new material with fresh threads.