As a martial artist I don't think full contact is the only way but semi-contact will do pretty much the same job with less risk of injury.
I am not 100% sure, but Wing-Chun where I live, is usually never full-contact, people wear pads, protectors or stop shortly before the body, which can look and be pretty ridiculous in a sparring match.
I think we can all agree that this way of training is better than no training at all since in a real situation, your body is pumped with adrenaline anyway.
I meant full-contact as in training with a resisting partner. Pads, no pads, some pads, fight club... whatever. There are obviously varying degrees of contact. For example, both MMA and Muay Thai have gloves and are considered full-contact (according to IFMA rules).
But what do you think about the techniques used ?
Tough question, I'm not sure how to answer that. IMO, there aren't really any stand-alone "techniques". So to me, it's like asking what I think about the entire system. In many aspects, it is simply about developing the punch.
Wing Chun at its core is more a way of training for fighting than it is a group of techniques or pre-determined answers. We build skill utilizing all of the concepts and principles of the system in unison, creating what I often refer to as an "action". Some of which are; adapt to the opponent, attack the attack, always pursue center, angle to take position, hands on top, attack and defense in a single action, responsive footwork, direct and efficient, etc… All of this is driven by mechanics that start with the vertical punch and proper elbow position.
In this way of thinking, potential applications are directly dependent on a greater and greater ability to implement the skills, concepts and structure of the system into a single reaction.