What is the cause of "speed wobbles"?
There is a lot of material online about the causes of speed wobbles, but I haven't seen spoke tension as a common cause.  It usually something created by, and stopped by, rider position rather than anything on the bike (I know you didn't want to read that).  

Just a thought though: wouldn't uneven spoke tension show up in the wheel not being "true"?

In any case, look up Jobst Brandt's book "The bicycle wheel".  It's the definitive text about this subject, written by a very meticulous engineer and cyclist. 

http://www.amazon.com/Bicycle-Wheel-3rd-Jobst-Brandt/dp/0960723668
http://sheldonbrown.com/brandt/