You only need to be as flexible as your sport/lifestyle requires, anymore is wasted and actually can be more dangerous.
Strength athletes often actually have a potential for a better range of motion, providing their mass does not interfere with it. Flexibity, or should I say the lack there of, is a safety mechanism by the body first and formost. WHat I mean by that is anyone of us, under sedation can literally be twisted into a pretzel. Another example would be putting one leg for ward up on a table at waist heigth. We can all do it and if we can put one up why cant we do the splits? There are a couple reasons, one is the muscles are used to contracting and kind of forget how to fully relaxe and legthen. The body also learns over time what range of motion we live in and adjust to set its safety standards to that range.
Exceeding things range requires a couple things, one is relaxation, another is speed and yet another is strength. Im sure many of you have stumbled or what not and pulled a muscle all while being no where near your limit of range. Your body takes into account the speed at which the limb is moving and will automatically contract the muscles in an effort to avoid the fall and save further bodily harm by possibly risking the muscle(ie muscle pull) which would often times heal much faster than your skill or even a tendon or ligament should the extreme range have been met. When you are stong you body is also more apt to allow you into an extreme range because the strength gives you more limb comtrol in that range. The speed aspect comes into play by voluntarily applying some speed to the movement when stretching (very controlled speed mind you) you are forcing a new adaptation and the body is basically relearning and readjusting its safety pattern for involuntarily contracting. If you relax enough, build strength in these extreme ranges of motion and work with speed of motion to get to these ranges, they can all go hand in hand to readapting.
I dont do much stretching any more but am gifted in the flexability department for the most part, I could be doing the side splits in less than 6 weeks if I wanted but my lifestyle doesnt require it.