I would also assume that bikes with low resistance coils would respond well to a relayed power circuit; the reduced power draw through the switches would make the entire electrical system more efficient.
I installed a solid-state regulator/rectifier (link in my sig) and installed a relay on the power to the coils. Those two mods greatly decreased the "cold bloodedness" of my CB650 and smoothed the engine out. I would assume the bike's lean-running nature makes ignition performance more noticeable, but improved ignition definitely can't hurt!
Having said that, the CB650's have a transistorized ignition from the factory. Do you have any experience with these units, and if so, how do they stack up to the HM Ignition?
All of the things you mention about improving current to the coils is true, provided the alternator can make the extra current to begin with...Japanese designers are notorious, even today, for little tricks like using downsized wire to increase the resistance voltage drops in the whole system so that the alternator does not have to be quite as large. Sometimes, though, they do this to the harm of the product: many of their cars have suffered in winter conditions as a result. The Toyotas before about 1995 are another example of this situation, and these bikes are no exception.
One thing to keep in mind when modifying Japanese electronics of any kind: they will design to use every last bit of power a [solid-state] part can muster, to save $0.0001 on the final product, then build millions of the [solid-state] parts and the product that uses it, to recover the engineering costs. That's just their mindset, always has been. So, if you go and increase power to such a unit, or used by such a unit ("I'm going to use 15 volt electrics", "I'm going to substitute 3-ohm coils for stock ones", etc.), you can quickly overload them and burn them out. I wish I had $5 for every time I've fixed a system damaged this way: I would not have to work today, anymore.
The Honda electronic ignitions have been much like their stock ignitions, in that they work pretty well when everything is 100% correct. But, dropping 10% of performance (i.e., battery voltage, bad contacts from age, bad/wrong plug caps) is enough to make the systems run poorly. They still run, just poorly. To "fix" them, you have to usually clean all connections and replace a bunch of parts, like plug caps, coils, wires, or plugs (or points and condensors). The CB650, CX500, Goldwing, and more, all fall into this category. A bad example: sub in a set of Dyna 2-ohm high-output coils on a Goldwing and take it to a dragstrip: you'll be lucky to run all night with it before it starts smoking the inline resistors for those coils. The wattage of the resistors is set to match only the stock coils of 2.5 to 3.0 ohms, and that last little bit of extra current cooks them. In short, to upgrade these bikes' electricals, you must always look further than just replacing one item: look at the whole system and make decisions based on the interaction of everything, or problems will crop up.
A classic example at SOHC4: using 3-ohm coils on a CB500/550. After 1 week of normal daily in-town riding, the battery voltage will drop to 12 volts or less. Throw in a halogen headlight and a #1157 taillite bulb (instead of the stock #1034), and it will be down to 11.5 volts and a very hot rectifier and alternator stator. The electric start begins to not turn the bike over unless the battery is externally charged (I've seen jumper posts added through sidecovers for nightly charging), the battery will fail over winter storage, and the rectifier will die after it heats up the connectors. The fuse will start blowing on irregular intervals. The problem: almost 3 amps of load have been added to the system, which is 2 more than the alternator can even generate at 13.6 volts. The system will slowly burn itself down while the owner becomes very unhappy, then sells or junks it, and tries it again on a different bike.
In all actuality, I'm seriously considering going into business, looking for these bikes that are in this situation, then rebuilding them correctly and educating the new owners. The first 3 of these are the Hondaman Special 750s, #1, #2, and #3. All 3 of the "source" bikes went through exactly this thing: the wiring harnesses were cooked. Next will be 500/550 bikes.
