Whoa!
I'd first said 'I presume..' because obviously a brake light/ pressure switch being added would be mentioned upfront. :(
A lighting coil that is marginally not up to output requirements, but otherwise operating OK will not have the symptom you are describing, namely a dimming of the headlight whether at 600 or 6000rpm:
the said dimming occurs weather I'm at full RPM or 600rpm
The marginal part would apply in this case as stated...one 35w front, and a taillight. Obviously a 30 watt coil hooked up to 75 watts-o-stuff isn't ever going to be bright.
I'd be looking at the voltage of the front bulb, for one. Maybe there is an error there. Disconnect the added 'pressure switch' and maybe the taillight, too.
BE CAREFUL about the disconnecting part...it's easy to disconnect the back wiring, say, in the headlight area...but you might also be disconnecting the regulator.
re: rewinding with the same wire size. The size of the wire is going to determine its current (amp) capability, the number of wraps and the density of the wrap will determine the voltage output. Point is, if you rewind using the same guage wire but wrap to a higher density/# of wraps, you will be expecting more current from the same thickness of wire.
The wire used is probably large enough to handle any reasonable increase in current, but keep in mind that you will be pushing more current through the same wire (if you use the same guage). It's not like you'll be winding something the size of a watermelon. ;)
This is a case of a LOT more not necessarily being better.
You'll need to pull the flywheel to get to the coil. Get a flywheel puller (about $10US). Note the LH threads! If you don't have an air tool (doing it by hand) you'll have to hold the flywheel whilst wrenching on it. Several ways to make your own, or use the transmission and brakes as a holder (not real effective that I've ever found).
Of general note:
http://www.buykawasaki.com/
is a good place to see how parts fit in your particular model. So would a service manual, of course.