Be careful when "doubling up" speaker cables as you are changing the characteristic impedance of the cable, probably for the worse unless done carefully. If using two runs of "zip cord" aka "monster" type wiring, you should arrange the wires so that they are reversed from each other when stacked. In other words, the negative wire on cable 1 would be stacked on top of the positive wire of cable 2 and vice-versa. Of course, you would have to connect them in the proper polarity at the amp and speakers. This minimizes inductance and will broaden the frequency response of the cables. This configuration is commonly known as a "star-quad". Two runs of 16 gauge wired in this fashion will give you a total of 13 gauge wire with a flatter response in the upper mids and treble than that of a standard 12 gauge cable. This way you get the better bass control of a larger wire but without sacrificing as much high frequency information.
As to Keith's original question, i'm wondering what your hoping to gain by changing speaker wires ? Do you feel the system is deficient in some way or are you just looking for more of a "good thing" ? : )
While i'm pretty familiar with the little Richmond's and liked them quite a bit for small speakers, i found them to sound very rich. Combined with tubes, things might be warm or laid back a little TOO much. As such, i would not look at the Audioquest cable that you mentioned. While it might be more than you were initially looking to spend, i would suggest either Kimber 4TC or Goertz MI-2's. Both can be found used relatively often and if you wait it out, sometimes for a steal. The Kimber will be leaner sounding with a little more "life" to it while the Goertz tends to sound seamless with a very natural balance to it. The drawback to the Goertz cables are that some amps go into fits with them, so you might have to use Zobel networks at the speakers' binding posts. These are supplied free of charge from a Goertz dealer or directly from Goertz. On top of this, the Goertz are flat copper ribbons that are not as flexible and harder to work with as compared to the very limber Kimbers. If you were interested in checking either of these out, Audio Advisor sells the Kimber with a 30 day return policy and Goertz does a 21 day trial at home deal via their website. Should you want to read up on the Goertz, i took the liberty of including their website info since it might be harder for you to find. Hope this helps... Sean