From a Sifu's perspective, having sparring matches against other schools/styles is all in presentation. Although sparring is not for everyone, school owners/Sifus (should) acknowledge that there are students who wish to test their "skills" in a dynamic environment. Facing someone from another style is an honest method to give you that "experience" against someone with a different set of techniques and ideas. It must be clear that this is not a test of Wing Chun against their style, your school against their school, your lineage against their lineage and so on. When I approach other school owners, I make this very clear. It is also important that everyone learns from the experience, hence we have one ring area and everyone watches a single match. Our intention is not to beat up the other group nor to pick winners and losers. It is to bring back the experience and look into what when wrong and what went right and see how to use the Kung Fu training to help the weak areas.
I have found this to be very good for my guys who want to spar. However, I also find it difficult for other schools to understand this concept. Traditional styles generally see it as a threat, as a blow to their ego if they do not do so well. Ironically, my point of view is that my guys learn MORE if they don't do so well. We video tape and review these sessions as well.
If there is no one to spar with, then it is difficult to spar outside your school. One should practice your kung fu more. Use the sparring as a gauge, come back to it after practicing a lot of Kung fu. Our Kung Fu offers you tools, like Chi Sao, to slow down and analyze many aspects of fighting.
Another thing to consider amongst schools is the insurance issues. This is why I feel that sparring, with students wearing protection gear, has it's purpose. My advice as the best way to prepare for "real life" situations is to become more confident in your abilities, play more Kung Fu so it becomes instinctive - no thinking. Sparring will help give you the experience to over come the "fears" of engaging with an unknown entity. However, the "life and death" aspect to a street fight is very difficult, if not impossible, to create in the kwoon. However, one must develop a warrior mentality, taking on the concept to not fear death but to put forth all they can be in a serious situation. The out come will always be the out come, as the truth will always be the truth.
Ving Tsun Kung Fu is a complete system. Those who reach the higher levels will understand and acknowledge this concept. It is the individual who strives for this completion, as Ving Tsun concepts are in everything.
Moy Yat Kung Fu - Martial Intelligence