Boxing can add a lot of spice to your wing chun. Also, the wing chun (for street use) can add some poweful garlic to your boxing.
However, you should be aware of one thing. Wing Chun and boxing are opposed to one another structurally.
Wing Chun stands on the immoveable elbow principle and the Center Line. It's cone principle comes from the center and flairs outward, while boxing is just the opposite. As your boxing character strenghtens, your wing chun character will be compromised. It is not so easy as just turning one on and then turning the other off. Right now, you have a bucket full of water. Your character is water. But now you will be adding ice cubes to the water. At first the ice cube melts into water. The character has not been changed. But then, something happens. The ice cubes begin to accumulate faster than they dissove. Pretty soon you have a bucket of ice and water. If you were to continue adding ice cubes, you would come to have a bucket of ice.
That's the bad news.
The good news is that you will also gain from the amalgamation of boxing and wing chun, a bucket of ice and water.
But, let's talk about Bruce for a moment. Early on, Bruce recognized the fluidity of Muhammed Ali (then Cassius Clay). He also saw something in Alli's footwork and timing that he was able to relate back to his core knowledge of wing chun (the timing and fluidity found in chi sao), at least at the highest levels.
The timing of beats, half beats, et all was already known to Bruce. He was amazed to see it used so well by Ali.
What he also liked about boxing was that the boxer remained dynamic, alive in his movement without getting stuck -- a sharp contrast to what he saw in other martial arts methods,and so apparant in karate tournaments.
Bruce went to work adding boxing highlights to his method and, with it, an increased punching arsenal. The boxing stuff was great for sparring and developing mobility and timing, but when the real thing would come about, where there was no ring and no rules, it would be his wing chun that he would depend on. This is merely to say that instead of dancing and jabbing and looking for an opening, he would be more apt to close the distance and control the fight up close which was, of course, his strong suit and home game. It was his "fighting character", not his sparring character.
By jamming down the opponent and becoming the other half of his center of gravity, he was able to open lines with multiple blast combinations while keeping on the pressure was his game (LOL, that is, if the opponent would stand and fight and didn't run).
Side note: You all know about the fight with Wong Jack Man, but do you know about the fight with the karate instructor from Japan? In this one, the karateka didn't run. He stood to make a fight as he was very, very skilled. Afterward, he told everyone that he had been in an automible accident.
From bobbing and weaving, Bruce was able to slip in some nice modifications to his infighting while still keeping on the pressure, sensitive to offsetting and destroying the opponent's structure while, himself, working from strong connection.
Anyway, another advantage to learning boxing is that it enables you to hide your wing chun character, and use it to trap your opponent both physically and psychologically. Most people know what a boxer looks like, so your opponent immediately recognizes your style, but then the wind suddenly changes. A new wind comes at him from out of nowhere, changing angles and tying him in knots, an experience outside his world. And it has arrived hard, and too fast for thought.
By working from a boxing/wing chun blend, and with some of your own modification, you will enjoy a number of interesting variables, like being able to make use of that wonderful hook while keeping on the physical pressure for disruption, And, being able to follow up with a good center line shot that due to the wing chun structure would be even faster than that of boxing.
I should also mention that is much easier when going to boxing from wing chun, then it is the other way around.
My recommomendation is that by all means. . do it!