I took a bit of EL wire and stripped off its outer jacket to reveal just the phosphor-coated copper wire, and used an alligator clip holding a single strand of wire to make the connection usually made by the tiny spiraled copper wires. Experiment details are after the video.

I used a signal generator set to 20 Vpp connected to a 1:10 (approximately) step-up transformer. Note that although I held the amplitude of the signal generator constant the voltage impressed across the wire assembly varied by about a factor of 3, almost certainly due to resonance effects involving the capacitance of the EL wire and the transformer secondary. It would be interesting to re-run the tests with feedback control keeping the secondary AC voltage constant as the drive frequency changes.

I was expecting the brightness and color change effects. I unjacketed the wire specifically to see how much of it would glow based on a single secondary contact, but I was not expecting the length of the glowing region to change. It's also somewhat curious that there appeared to be "breaks" in the phosphor in that if the secondary wire was on one side of the break it would not glow on the other wide even if well within the range of glow effect expected given the frequency. (I put "break" in scare quotes because I couldn't actually see anything different in the wire with my naked eye.)

Future experiments:

• Regulate transformer secondary voltage, not primary, to remove the resonant voltage boost as a confounding factor in determining brightness.

• Examine effects of harmonic content. Getting these through the transformer may be a challenge. I was using a wall wart transformer backward to get the voltage boost, so using a transformer optimized for a wider frequency range may help with this. Driving with a square wave instead of a sine wave produced brighter output, but I was not correcting for the increase in RMS voltage.
• Examine a longer segment of wire to see if the "breaks" in the phosphor are a regular occurrence, possibly due to manufacturing technique.
• Crease the wire to see if I can induce a "break" in the phosphor.
• See if varying the frequency of intact wire can induce a "candy-cane" striping effect with the glow only following the course of the secondary wires. (Please, if you experiment with this and come up with an effect that's the rage at burning man next year or something, drop me a kind word, preferably publicly. Thanks!)