Several things are interesting about your post.
First: "However I wonder if the positive effects of the Valsalva maneuver are good enough reason to use the technique considering the possible negative implications such as syncope, stroke, blown aneursym (sic) or death. I assume that these possible implications are the result of heightened blood pressure."
The incidence of training-associated cerebrovascular accident (CVA) in the weight room is so low as to be statistically unmeasurable. We have done a thorough search of the literature and there is a complete absence of any documented case of stroke during barbell training. There are, however, lots of back injuries. Which eventuality would you rather prepare for? As for a blown aneurysm, first you have to have an aneurysm to blow one out, and THAT is always just plain old bad luck (despite the fact that the incidence of weight training-associated aneurysm dissections is also statistically insignificant).
Second: "I have definitely had a headache after heavy deadlifts before and have most definitely seen stars after a set of squats. Were those occurrences a result of the Valsalva?"
I don't know. But headache and death are certainly two unrelated phenomena. I've had lots of headaches that were associated with Guinness, during the consumption of which no Valsalva or deadlifting occurred.
Third: "By the way, you said in your book to hold your breath during each of your heavy reps, but I have heard differing opinions on the matter. I have heard the ever common "inhale as you go down, exhale as you go up", "only use the Valsalva for 2-3 seconds as your go through your sticking point", and "do not consciously think about breathing or the Valsalva during exercise as it will come naturally".
Which one do you think Andy Bolton used during his world record 1003 lb. deadlift? It makes absolutely no difference what the NASM, the ACSM, the NSCA, AFAA, ACE, the YMCA, or Pat Robertson thinks about how one ought to breathe during exercise. The fact is that every heavy deadlift that has ever been pulled off the floor was done with some form of a Valsalva, and the death toll fails to mount. What does this tell you about the safety of the Valsalva for your workout this afternoon? The last remark about the Valsalva coming naturally is correct, but a 1003 deadlift is not "natural" in the commonly understood sense of the word, and the Valsalva that accompanied it was not "natural" either -- it was deliberate, thorough, and lasted for the whole deadlift. The inexperienced, lawyer-spooked fools at the certification organizations can issue any position papers they like, but the fact remains that as long as heavy weights are being lifted, people will be holding their breath while they do it, and everybody will be just fine if they don't hurt their backs or pull a hamstring.
Furthermore, Mr. Bolton was adapted to both a very goddamn heavy deadlift and a deliberate, thorough, and long Valsalva manuver, because he'd trained for it. He didn't just wander in off the street, and neither have you. Since tissues adapt to stress, the stress of a Valsalva is adapted to by whatever structures are subjected to the stress as the intensity of the load accumulates, just like the spine, the ligaments holding the spine together, and the muscles that keep the spine straight have that make the deadlift possible. This fact -- that adaptation occurs in response to exercise in all affected tissues -- along with the fact that lots of people have lifted heavy weights with no known incidence of stroke, even in the absence of an explanation for why, should provide solace and balm for your furrowed brow.