OP,
For the money, it's hard to beat the amount of light you can get with HID. The price of these things has come down so much it's pretty hard to believe.
If you do decide to go the route of HID, please consider limiting yourself to the 35W setups rather than the 55W.
The way HID work is exactly like any other florescent bulb..... there is a ballast that has to charge to a high voltage to make the arc in the bulb. Once the arc has happened a number of times, the gas remains energized enough that it doesn't take a lot of power to make it arc again. Until then, the HID uses far more power than the number stated on the literature. 3-5 times as much, for some number of seconds as it warms up. One 35W HID is going to draw about the same power as both OEM 55W halogen bulbs would, for that start up period. The electrical engineers at Kawasaki designed the charging system with that much load in mind. Should last the life of the bike.
2 35W bulbs place some strain on the charging system if you start them at the same time. 55W bulbs, single or double, definitely put some stress on the charging system.
This is an issue for a motorcycle charging system, as there is very little excess power available. The power all comes from the alternator, and any excess gets stored in the battery for future use up to the point where the battery is fully charged. Because sport bikes are as light as possible, the margin is even thinner here, than it is with touring machines and the like.
When you hear about people having to replace the stator, that's almost always due to drawing more power than the bike can make. Whatever the HID may need, the battery will loan out. The budget has to be balanced by the alternator, which has to work harder, to replenish the charge. The alternator is made of two parts. The rotor, and the stator. The stator is static..... sits in one place. As the ends of the rotor pass it, the magnetic lines of force shove electrons off the wires in the stator windings. That is where the current flow comes from. It isn't without some work being done, which results in heat being generated in the windings.
The only way for the stator to cool off, is to pass that heat to the engine oil that is splashed around on the windings by the rotor. The oil falls back to the bottom of the case, and then gets returned to the pan/pump/lube system. The hardest part of the stator to cool, is the point furthest away from the bottom. Heat rises, gravity drains the oil away from that point the most..... it stays hotter longer. The stator fails due to the melting of the insulation between the windings on the poles. As the insulation melts, the wires short together.... that makes that part of the winding produce less current. The demand doesn't change so the alternator has to keep producing power anyway, but now it has to do it for a longer period of time..... which means it gets even hotter, which melts more insulation, etc., etc.